diff --git a/.gitignore b/.gitignore
index c5e9682..162c415 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,9 @@
 *.py[co]
 .*.sw?
+.DS_Store
 /reclass-config.yml
 /reclass.egg-info
 /build
 /dist
 /.coverage
+.kitchen
diff --git a/.kitchen-verify.sh b/.kitchen-verify.sh
new file mode 100755
index 0000000..fb3adde
--- /dev/null
+++ b/.kitchen-verify.sh
@@ -0,0 +1,22 @@
+#!/bin/bash
+#set -x
+
+# setup
+source /*.env
+INVENTORY_BASE_URI=/tmp/kitchen/test/model/$MODEL
+RECLASS=/tmp/kitchen
+
+# prereq
+python -m ensurepip --default-pip
+pip install pipenv
+
+# env
+cd $RECLASS
+pipenv --venv || pipenv install --python ${PYVER}
+test -e /etc/reclsss || mkdir /etc/reclass
+cp -avf $INVENTORY_BASE_URI/reclass-config* /etc/reclass
+
+# verify
+for n in $(ls $INVENTORY_BASE_URI/nodes/*|sort); do
+  pipenv run python${PYVER} ./reclass.py --inventory-base-uri=$INVENTORY_BASE_URI --nodeinfo $(basename $n .yml)
+done
diff --git a/.kitchen.yml b/.kitchen.yml
new file mode 100644
index 0000000..45be629
--- /dev/null
+++ b/.kitchen.yml
@@ -0,0 +1,41 @@
+---
+driver:
+  name: docker
+  priviledged: false
+  use_sudo: false
+  volume:
+    - <%= ENV['PWD'] %>:/tmp/kitchen
+
+
+provisioner:
+  name: shell
+  script: .kitchen-verify.sh
+
+
+verifier:
+  name: inspec
+
+<%- pyver = ENV['PYTHON_VERSION'] || '2.7' %>
+
+platforms:
+  <% `find test/model -maxdepth 1 -mindepth 1 -type d |sort -u`.split().each do |model| %>
+  <% model=model.split('/')[2] %>
+  - name: <%= model %>
+    driver_config:
+      image: python:<%= pyver %>
+      platform: ubuntu
+      hostname: reclass
+      provision_command:
+        #FIXME, setup reclass env (prereq, configs, upload models)
+        #- apt-get install -y rsync
+        - echo "
+            export LC_ALL=C.UTF-8;\n
+            export LANG=C.UTF-8;\n
+            export PYVER=<%= pyver %>;\n
+            export MODEL=<%= model %>;\n
+          " > /kitchen.env
+  <% end %>
+
+suites:
+  - name: model
+
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..2a41776
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,116 @@
+sudo: required
+language: python
+dist: trusty
+cache: pip
+python:
+- '2.7'
+- '3.6'
+service:
+- docker
+
+#apt:
+  #update: true
+
+#stages:
+#- name: test
+#- name: coverage
+#- name: models
+#- name: build
+#  if: fork = false
+#- name: publish
+#  if: tag =~ ^v.* and fork = false and branch = 'master'
+
+env:
+  global:
+    - PACKAGENAME="reclass"
+
+install: &pyinst
+- pip install pyparsing
+- pip install PyYAML
+# To test example models with kitchen:
+- |
+  test -e Gemfile || cat <<EOF > Gemfile
+  source 'https://rubygems.org'
+  gem 'rake'
+  gem 'test-kitchen'
+  gem 'kitchen-docker'
+  gem 'kitchen-inspec'
+  gem 'inspec'
+- bundle install
+
+script:
+- python setup.py install
+- find . reclass -name 'test_*.py' | sort | xargs -n1 -i% bash -c "echo %; python %"
+# To test example models with kitchen:
+- export PYTHON_VERSION=$TRAVIS_PYTHON_VERSION
+- kitchen list
+- if [ "$PYTHON_VERSION" = "2.7" ]; then kitchen test; fi
+
+# NOTE: travis stage builds, below saved for future reference
+#jobs:
+#  include:
+#  - stage: test
+#    script: &unittest
+#    - python setup.py install
+#    - find . reclass -name 'test_*.py' | sort | xargs -n1 -i% bash -c "echo %; python %"
+#
+#  - stage: coverage
+#    install: *pyinst
+#    script:
+#    - python3 -m pytest --cov=. --cov-report=term-missing:skip-covered
+#    - coverage xml
+#    #- coveralls
+#    #- |
+#        #[ ! -z "${CODACY_PROJECT_TOKEN}" ] && python-codacy-coverage -r coverage.xml || echo "Codacy coverage NOT exported"
+#
+#  - stage: lint
+#    script:
+#    - python3 -m flake8
+#
+#  - stage: models
+#    install: &kitchen
+#    - pip install PyYAML
+#    - pip install virtualenv
+#    - |
+#      test -e Gemfile || cat <<EOF > Gemfile
+#      source 'https://rubygems.org'
+#      gem 'rake'
+#      gem 'test-kitchen'
+#      gem 'kitchen-docker'
+#      gem 'kitchen-inspec'
+#      gem 'inspec'
+#    - bundle install
+#    script:
+#    - export PYTHON_VERSION=$TRAVIS_PYTHON_VERSION
+#    - kitchen list
+#    #FIXME- kitchen test
+#
+#  - stage: build
+#    install: *pyinst
+#    script: []
+#
+#  - stage: publish
+#    install:
+#    - "/bin/true"
+#    script:
+#    - "/bin/true"
+#    deploy:
+#      provider: pypi
+#      user: epcim
+#      password:
+#        secure: TBD
+#      on:
+#        tags: true
+#        repo: salt-formulas/reclass
+#        branch: master
+#        #FIXME, $TRAVIS_PYTHON_VERSION == '2.7'
+
+notifications:
+  webhooks:
+    on_success: change  # options: [always|never|change] default: always
+    on_failure: never
+    on_start: never
+    on_cancel: never
+    on_error: never
+  email: true
+
diff --git a/MANIFEST.in b/MANIFEST.in
new file mode 100644
index 0000000..1f4c27b
--- /dev/null
+++ b/MANIFEST.in
@@ -0,0 +1,14 @@
+# Include the license and changelog
+include LICENSE ChangeLog.rst
+# Exclude development tooling
+exclude Makefile requirements.txt .pylintrc  reclass.py
+# Exclude testing infra
+exclude run_tests.py
+prune reclass/tests
+prune reclass/datatypes/tests
+prune reclass/storage/tests
+prune reclass/utils/tests
+prune reclass/values/tests
+# Exclude "source only" content
+prune doc
+prune examples
diff --git a/Pipfile b/Pipfile
new file mode 100644
index 0000000..525e7cc
--- /dev/null
+++ b/Pipfile
@@ -0,0 +1,17 @@
+[[source]]
+url = "https://pypi.python.org/simple"
+verify_ssl = true
+name = "pypi"
+
+[dev-packages]
+
+[packages]
+pyparsing = "*"
+PyYAML = "*"
+six = "*"
+pyyaml = "*"
+# FIXME, issues with compile phase
+#"pygit2" = "*"
+
+[requires]
+python_version = "2.7"
diff --git a/README-extentions.rst b/README-extentions.rst
new file mode 100644
index 0000000..61364a4
--- /dev/null
+++ b/README-extentions.rst
@@ -0,0 +1,457 @@
+Escaping of References and Inventory Queries
+--------------------------------------------
+
+Reference and inventory queries can be escaped to produce literal strings, for example:
+
+.. code-block:: yaml
+
+  parameters:
+    colour: Blue
+    unescaped: The colour is ${colour}
+    escaped: The colour is \${colour}
+    double_escaped: The colour is \\${colour}
+
+
+This would produce:
+
+.. code-block:: yaml
+
+  parameters:
+    colour: Blue
+    unescaped: The colour is Blue
+    escaped: The colour is ${colour}
+    double_escaped: The colour is \Blue
+
+
+
+Ignore class not found
+----------------------
+
+At some cases (bootstrapping, development) it can be convenient to ignore some missing classes.
+To control the feature there are two options available:
+
+.. code-block:: yaml
+
+  ignore_class_notfound: False
+  ignore_class_regexp: ['.*']
+
+If you set regexp pattern to ``service.*`` all missing classes starting 'service.' will be logged with warning, but will not
+fail to return rendered reclass. Assuming all parameter interpolation passes.
+
+
+
+Merging Referenced Lists and Dictionaries
+-----------------------------------------
+
+Referenced lists or dicts can now be merged:
+
+.. code-block:: yaml
+
+  # nodes/test.yml
+  classes:
+    - test1
+    - test2
+  parameters:
+    one:
+      a: 1
+      b: 2
+    two:
+      c: 3
+      d: 4
+    three:
+      e: 5
+
+  # classes/test1.yml
+  parameters:
+    three: ${one}
+
+  # classes/test2.yml
+  parameters:
+    three: ${two}
+
+``running reclass.py --nodeinfo node1`` then gives:
+
+.. code-block:: yaml
+
+  parameters:
+    one:
+      a: 1
+      b: 2
+    three:
+      a: 1
+      b: 2
+      c: 3
+      d: 4
+      e: 5
+    two:
+      c: 3
+      d: 4
+
+This first sets the parameter three to the value of parameter one (class test1) then merges parameter two into
+parameter three (class test2) and finally merges the parameter three definition given in the node definition into
+the final value.
+
+
+Allow override list and dicts by empty entity,None instead of merge
+-------------------------------------------------------------------
+
+With settings:
+
+.. code-block:: yaml
+
+  allow_none_override: True       # default True
+
+  # note dict,list over None is allowed and not configurable
+
+Referenced lists or dicts can now be overriden by None or empty type of dict, list:
+
+.. code-block:: yaml
+
+  # nodes/test.yml
+  parameters:
+    one:
+      a: 1
+      b: 2
+    two: {}
+    three: None
+
+  # classes/test1.yml
+  parameters:
+    one: ${two}
+
+  # classes/test2.yml
+  parameters:
+    three: ${one}
+
+
+Nested References
+-----------------
+
+References can now be nested, for example:
+
+.. code-block:: yaml
+
+  # nodes/node1.yml
+  parameters:
+    alpha:
+      one: ${beta:${alpha:two}}
+      two: a
+    beta:
+      a: 99
+
+``reclass.py --nodeinfo node1`` then gives:
+
+.. code-block:: yaml
+
+  parameters:
+    alpha:
+      one: 99
+      two: a
+    beta:
+      a: 99
+
+The ``${beta:${alpha:two}}`` construct first resolves the ``${alpha:two}`` reference to the value 'a', then resolves
+the reference ``${beta:a}`` to the value 99.
+
+
+Ignore overwritten missing references
+-------------------------
+
+Given the following classes:
+
+.. code-block:: yaml
+  # node1.yml
+  classes:
+  - class1
+  - class2
+  - class3
+
+  # class1.yml
+  parameters:
+    a: ${x}
+
+  # class2.yml
+  parameters:
+    a: ${y}
+
+  # class3.yml
+  parameters:
+    y: 1
+
+  
+The parameter ``a`` only depends on the parameter ``y`` through the reference set in class2. The fact that the parameter ``x`` referenced
+in class1 is not defined does not affect the final value of the parameter ``a``. For such overwritten missing references by default a warning is
+printed but no error is raised, providing the final value of the parameter being evaluated is a scalar. If the final value is a dictionary or list
+an error will always be raised in the case of a missing reference.
+
+Default value is True to keep backward compatible behavior.
+
+.. code-block:: yaml
+
+  ignore_overwritten_missing_reference: True
+
+
+Print summary of missed references
+----------------------------------
+
+Instead of failing on the first undefinded reference error all missing reference errors are printed at once.
+
+.. code-block:: yaml
+  reclass --nodeinfo mynode
+  -> dontpanic
+     Cannot resolve ${_param:kkk}, at mkkek3:tree:to:fail, in yaml_fs:///test/classes/third.yml
+     Cannot resolve ${_param:kkk}, at mkkek3:tree:another:xxxx, in yaml_fs:///test/classes/third.yml
+     Cannot resolve ${_param:kkk}, at mykey2:tree:to:fail, in yaml_fs:///test/classes/third.yml
+
+.. code-block:: yaml
+
+  group_errors: True
+
+
+Use references in class names
+-----------------------------
+
+Allows to use references in the class names.
+
+References pointed to in class names cannot themselves reference another key, they should be simple strings.
+
+To avoid pitfalls do not over-engineer your class references. They should be used only for core conditions and only for them.
+A short example: `- system.wrodpress.db.${_class:database_backend}`.
+
+Best practices:
+- use references in class names always load your global class specification prior the reference is used.
+- structure your class references under parameters under one key (for example `_class`).
+- use class references as a kind of "context" or "global" available options you always know what they are set.
+
+Class referencing for existing reclass users. Frequently when constructing your models you had to load or not load some
+classes based on your setup. In most cases this lead to fork of a model or introducing kind of template generator (like cookiecutter) to
+create a model based on the base "context" or "global" variables. Class referencing is a simple way how to avoid
+"pre-processors" like this and if/else conditions around class section.
+
+
+Assuming following class setup:
+
+* node is loading `third.yml` class only
+
+
+Classes:
+
+.. code-block:: yaml
+  #/etc/reclass/classes/global.yml
+  parameters:
+    _class:
+      env:
+        override: 'env.dev'
+    lab:
+      name: default
+
+  #/etc/reclass/classes/lab/env/dev.yml
+  parameters:
+    lab:
+      name: dev
+
+  #/etc/reclass/classes/second.yml
+  classes:
+    - global
+    - lab.${_class:env:override}
+
+  #/etc/reclass/classes/third.yml
+  classes:
+    - global
+    - second
+
+
+Reclass --nodeinfo then returns:
+
+.. code-block:: yaml
+
+  ...
+  ...
+  applications: []
+  environment: base
+  exports: {}
+  classes:
+  - global
+  - lab.${_class:env:override}
+  - second
+  parameters:
+    _class:
+      env:
+        override: env.dev
+    lab:
+      name: dev
+    ...
+    ...
+
+
+Inventory Queries
+-----------------
+
+Inventory querying works using a new key type - exports to hold values which other node definitions can read using a $[] query, for example with:
+
+.. code-block:: yaml
+
+  # nodes/node1.yml
+  exports:
+    test_zero: 0
+    test_one:
+      name: ${name}
+      value: 6
+    test_two: ${dict}
+
+  parameters:
+    name: node1
+    dict:
+      a: 1
+      b: 2
+    exp_value_test: $[ exports:test_two ]
+    exp_if_test0: $[ if exports:test_zero == 0 ]
+    exp_if_test1: $[ exports:test_one if exports:test_one:value == 7 ]
+    exp_if_test2: $[ exports:test_one if exports:test_one:name == self:name ]
+
+  # nodes/node2.yml
+  exports:
+    test_zero: 0
+    test_one:
+      name: ${name}
+      value: 7
+    test_two: ${dict}
+
+  parameters:
+    name: node2
+    dict:
+      a: 11
+      b: 22
+
+
+``running reclass.py --nodeinfo node1``  gives (listing only the exports and parameters):
+
+.. code-block:: yaml
+
+  exports:
+    test_one:
+      name: node1
+      value: 6
+    test_two:
+      a: 1
+      b: 2
+  parameters:
+    dict:
+      a: 1
+      b: 2
+    exp_if_test0:
+      - node1
+      - node2
+    exp_if_test1:
+      node2:
+        name: node2
+        value: 7
+    exp_if_test2:
+      node1:
+        name: node1
+        value: 6
+    exp_value_test:
+      node1:
+        a: 1
+        b: 2
+      node2:
+        a: 11
+        b: 22
+    name: node1
+
+
+Exports defined for a node can be a simple value or a reference to a parameter in the node definition.
+The ``$[]`` inventory queries are calculated for simple value expressions, ``$[ exports:key ]``, by returning
+a dictionary with an element (``{ node_name: key value }``) for each node which defines 'key' in the exports
+section. For tests with a preceeding value, ``$[ exports:key if exports:test_key == test_value ]``, the
+element (``{ node_name: key value }``) is only added to the returned dictionary if the test_key defined in
+the node exports section equals the test value. For tests without a preceeding value,
+``$[ if exports:test_key == test_value ]``, a list of nodes which pass the test is returned. For either test
+form the test value can either be a simple value or a node parameter. And as well as an equality test
+a not equals test (``!=``) can also be used.
+
+
+**Inventory query options**
+
+By default inventory queries only look at nodes in the same environment as the querying node. This can be
+overriden using the +AllEnvs option:
+
+.. code-block:: yaml
+
+  $[ +AllEnvs exports:test ]
+
+Any errors in rendering the export parameters for a node will give an error for the inventory query as a whole.
+This can be overriden using the ``+IgnoreErrors`` option:
+
+.. code-block:: yaml
+
+  $[ +IgnoreErrors exports:test ]
+
+With the ``+IgnoreErrors`` option nodes which generate an error evaluating ``exports:test`` will be ignored.
+
+Inventory query options can be combined:
+
+.. code-block:: yaml
+
+  $[ +AllEnvs +IgnoreErrors exports:test ]
+
+**Logical operators and/or**
+
+The logical operators and/or can be used in inventory queries:
+
+.. code-block:: yaml
+
+  $[ exports:test_value if exports:test_zero == 0 and exports:test_one == self:value ]
+
+The individual elements of the if statement are evaluated and combined with the logical operators starting from the
+left and working to the right.
+
+
+**Inventory query example**
+
+Defining a cluster of machines using an inventory query, for example to open access to a database server to a
+group of nodes. Given exports/parameters for nodes of the form:
+
+.. code-block:: yaml
+
+  # for all nodes requiring access to the database server
+    exports:
+      host:
+        ip_address: aaa.bbb.ccc.ddd
+      cluster: _some_cluster_name_
+
+.. code-block:: yaml
+
+  # for the database server
+  parameters:
+    cluster_name: production-cluster
+    postgresql:
+      server:
+        clients: $[ exports:host:ip_address if exports:cluster == self:cluster_name ]
+
+This will generate a dictionary with an entry for node where the ``export:cluster`` key for a node is equal to the
+``parameter:cluster_name`` key of the node on which the inventory query is run on. Each entry in the generated dictionary
+will contain the value of the ``exports:host:ip_address`` key. The output dictionary (depending on node definitions)
+would look like:
+
+.. code-block:: yaml
+
+  node1:
+    ip_address: aaa.bbb.ccc.ddd
+  node2:
+    ip_address: www.xxx.yyy.zzz
+
+For nodes where exports:cluster key is not defined or where the key is not equal to self:cluster_name no entry is made
+in the output dictionary.
+
+In practise the exports:cluster key can be set using a parameter reference:
+
+.. code-block:: yaml
+
+  exports:
+    cluster: ${cluster_name}
+  parameters:
+    cluster_name: production-cluster
+
+The above exports and parameter definitions could be put into a separate class and then included by nodes which require
+access to the database and included by the database server as well.
diff --git a/README.rst b/README.rst
index e88c135..99de5f6 100644
--- a/README.rst
+++ b/README.rst
@@ -1,5 +1,26 @@
-reclass README
-==============
+Reclass README
+=========================
 
-The documentation for **reclass** is available from
-http://reclass.pantsfullofunix.net.
+This is the fork of original **reclass** that is available at:
+https://github.com/madduck/reclass
+
+Extentions
+==========
+
+List of the core features:
+
+* Escaping of References and Inventory Queries
+* Merging Referenced Lists and Dictionaries
+* Nested References
+* Inventory Queries
+* Ignore class notfound/regexp option
+
+
+.. include:: ./README-extensions.rst
+
+
+Documentation
+=============
+
+Documentation covering the original version is in the doc directory.
+See the README-extensions.rst file for documentation on the extentions.
diff --git a/doc/source/conf.py b/doc/source/conf.py
index 422128e..6ce7f02 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -16,7 +16,7 @@
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
-#sys.path.insert(0, os.path.abspath('.'))
+sys.path.insert(0, os.path.abspath('../../'))
 
 # -- General configuration -----------------------------------------------------
 
diff --git a/reclass/__init__.py b/reclass/__init__.py
index 7cd6c30..a79c8e1 100644
--- a/reclass/__init__.py
+++ b/reclass/__init__.py
@@ -7,16 +7,19 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 
-from output import OutputLoader
-from storage.loader import StorageBackendLoader
-from storage.memcache_proxy import MemcacheProxy
+from reclass.output import OutputLoader
+from reclass.storage.loader import StorageBackendLoader
+from reclass.storage.memcache_proxy import MemcacheProxy
+
 
 def get_storage(storage_type, nodes_uri, classes_uri, **kwargs):
     storage_class = StorageBackendLoader(storage_type).load()
     return MemcacheProxy(storage_class(nodes_uri, classes_uri, **kwargs))
 
+def get_path_mangler(storage_type,**kwargs):
+    return StorageBackendLoader(storage_type).path_mangler()
 
-def output(data, fmt, pretty_print=False):
+def output(data, fmt, pretty_print=False, no_refs=False):
     output_class = OutputLoader(fmt).load()
     outputter = output_class()
-    return outputter.dump(data, pretty_print=pretty_print)
+    return outputter.dump(data, pretty_print=pretty_print, no_refs=no_refs)
diff --git a/reclass/adapters/ansible.py b/reclass/adapters/ansible.py
index cbf5f17..f6e9af3 100755
--- a/reclass/adapters/ansible.py
+++ b/reclass/adapters/ansible.py
@@ -10,15 +10,21 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+# 2017.08.08 Andew Pickford <anpickford@googlemail.com>
+# The ansible adapter has received little testing and may not work at all now.
+
 
 import os, sys, posix, optparse
 
+from six import iteritems
+
 from reclass import get_storage, output
 from reclass.core import Core
 from reclass.errors import ReclassException
 from reclass.config import find_and_read_configfile, get_options
 from reclass.version import *
 from reclass.constants import MODE_NODEINFO
+from reclass.settings import Settings
 
 def cli():
     try:
@@ -27,6 +33,7 @@
         ansible_dir = os.path.abspath(os.path.dirname(sys.argv[0]))
 
         defaults = {'inventory_base_uri': ansible_dir,
+                    'no_refs' : False,
                     'pretty_print' : True,
                     'output' : 'json',
                     'applications_postfix': '_hosts'
@@ -54,10 +61,11 @@
                               add_options_cb=add_ansible_options_group,
                               defaults=defaults)
 
-        storage = get_storage(options.storage_type, options.nodes_uri,
-                              options.classes_uri)
+        storage = get_storage(options.storage_type, options.nodes_uri, options.classes_uri)
         class_mappings = defaults.get('class_mappings')
-        reclass = Core(storage, class_mappings)
+        defaults.update(vars(options))
+        settings = Settings(defaults)
+        reclass = Core(storage, class_mappings, settings)
 
         if options.mode == MODE_NODEINFO:
             data = reclass.nodeinfo(options.hostname)
@@ -75,13 +83,13 @@
             apps = data['applications']
             if options.applications_postfix:
                 postfix = options.applications_postfix
-                groups.update([(k + postfix, v) for k,v in apps.iteritems()])
+                groups.update([(k + postfix, v) for (k, v) in iteritems(apps)])
             else:
                 groups.update(apps)
 
             data = groups
 
-        print output(data, options.output, options.pretty_print)
+        print output(data, options.output, options.pretty_print, options.no_refs)
 
     except ReclassException, e:
         e.exit_with_message(sys.stderr)
diff --git a/reclass/adapters/salt.py b/reclass/adapters/salt.py
index 1b45823..31179ff 100755
--- a/reclass/adapters/salt.py
+++ b/reclass/adapters/salt.py
@@ -9,13 +9,15 @@
 
 import os, sys, posix
 
-from reclass import get_storage, output
+from six import iteritems
+
+from reclass import get_storage, output, get_path_mangler
 from reclass.core import Core
 from reclass.errors import ReclassException
-from reclass.config import find_and_read_configfile, get_options, \
-        path_mangler
+from reclass.config import find_and_read_configfile, get_options
 from reclass.constants import MODE_NODEINFO
 from reclass.defaults import *
+from reclass.settings import Settings
 from reclass.version import *
 
 def ext_pillar(minion_id, pillar,
@@ -24,16 +26,17 @@
                nodes_uri=OPT_NODES_URI,
                classes_uri=OPT_CLASSES_URI,
                class_mappings=None,
-               propagate_pillar_data_to_reclass=False):
+               propagate_pillar_data_to_reclass=False,
+               **kwargs):
 
-    nodes_uri, classes_uri = path_mangler(inventory_base_uri,
-                                          nodes_uri, classes_uri)
-    storage = get_storage(storage_type, nodes_uri, classes_uri,
-                          default_environment='base')
+    path_mangler = get_path_mangler(storage_type)
+    nodes_uri, classes_uri = path_mangler(inventory_base_uri, nodes_uri, classes_uri)
+    storage = get_storage(storage_type, nodes_uri, classes_uri)
     input_data = None
     if propagate_pillar_data_to_reclass:
         input_data = pillar
-    reclass = Core(storage, class_mappings, input_data=input_data)
+    settings = Settings(kwargs)
+    reclass = Core(storage, class_mappings, settings, input_data=input_data)
 
     data = reclass.nodeinfo(minion_id)
     params = data.get('parameters', {})
@@ -47,14 +50,13 @@
 
 def top(minion_id, storage_type=OPT_STORAGE_TYPE,
         inventory_base_uri=OPT_INVENTORY_BASE_URI, nodes_uri=OPT_NODES_URI,
-        classes_uri=OPT_CLASSES_URI,
-        class_mappings=None):
+        classes_uri=OPT_CLASSES_URI, class_mappings=None, **kwargs):
 
-    nodes_uri, classes_uri = path_mangler(inventory_base_uri,
-                                          nodes_uri, classes_uri)
-    storage = get_storage(storage_type, nodes_uri, classes_uri,
-                          default_environment='base')
-    reclass = Core(storage, class_mappings, input_data=None)
+    path_mangler = get_path_mangler(storage_type)
+    nodes_uri, classes_uri = path_mangler(inventory_base_uri, nodes_uri, classes_uri)
+    storage = get_storage(storage_type, nodes_uri, classes_uri)
+    settings = Settings(kwargs)
+    reclass = Core(storage, class_mappings, settings, input_data=None)
 
     # if the minion_id is not None, then return just the applications for the
     # specific minion, otherwise return the entire top data (which we need for
@@ -68,7 +70,7 @@
     else:
         data = reclass.inventory()
         nodes = {}
-        for node_id, node_data in data['nodes'].iteritems():
+        for (node_id, node_data) in iteritems(data['nodes']):
             env = node_data['environment']
             if env not in nodes:
                 nodes[env] = {}
@@ -81,6 +83,7 @@
     try:
         inventory_dir = os.path.abspath(os.path.dirname(sys.argv[0]))
         defaults = {'pretty_print' : True,
+                    'no_refs' : False,
                     'output' : 'yaml',
                     'inventory_base_uri': inventory_dir
                    }
@@ -95,6 +98,12 @@
                               nodeinfo_help='output pillar data for a specific node',
                               defaults=defaults)
         class_mappings = defaults.get('class_mappings')
+        defaults.update(vars(options))
+        defaults.pop("storage_type", None)
+        defaults.pop("inventory_base_uri", None)
+        defaults.pop("nodes_uri", None)
+        defaults.pop("classes_uri", None)
+        defaults.pop("class_mappings", None)
 
         if options.mode == MODE_NODEINFO:
             data = ext_pillar(options.nodename, {},
@@ -102,16 +111,18 @@
                               inventory_base_uri=options.inventory_base_uri,
                               nodes_uri=options.nodes_uri,
                               classes_uri=options.classes_uri,
-                              class_mappings=class_mappings)
+                              class_mappings=class_mappings,
+                              **defaults)
         else:
             data = top(minion_id=None,
                        storage_type=options.storage_type,
                        inventory_base_uri=options.inventory_base_uri,
                        nodes_uri=options.nodes_uri,
                        classes_uri=options.classes_uri,
-                       class_mappings=class_mappings)
+                       class_mappings=class_mappings,
+                       **defaults)
 
-        print output(data, options.output, options.pretty_print)
+        print output(data, options.output, options.pretty_print, options.no_refs)
 
     except ReclassException, e:
         e.exit_with_message(sys.stderr)
diff --git a/reclass/cli.py b/reclass/cli.py
index 5666e16..f0b6069 100644
--- a/reclass/cli.py
+++ b/reclass/cli.py
@@ -11,35 +11,36 @@
 
 from reclass import get_storage, output
 from reclass.core import Core
+from reclass.settings import Settings
 from reclass.config import find_and_read_configfile, get_options
-from reclass.errors import ReclassException
 from reclass.defaults import *
+from reclass.errors import ReclassException
 from reclass.constants import MODE_NODEINFO
 from reclass.version import *
 
 def main():
     try:
-        defaults = {'pretty_print' : OPT_PRETTY_PRINT,
+        defaults = {'no_refs' : OPT_NO_REFS,
+                    'pretty_print' : OPT_PRETTY_PRINT,
                     'output' : OPT_OUTPUT
                    }
         defaults.update(find_and_read_configfile())
-        options = get_options(RECLASS_NAME, VERSION, DESCRIPTION,
-                              defaults=defaults)
 
-        storage = get_storage(options.storage_type, options.nodes_uri,
-                              options.classes_uri, default_environment='base')
+        options = get_options(RECLASS_NAME, VERSION, DESCRIPTION, defaults=defaults)
+        storage = get_storage(options.storage_type, options.nodes_uri, options.classes_uri)
         class_mappings = defaults.get('class_mappings')
-        reclass = Core(storage, class_mappings)
+        defaults.update(vars(options))
+        settings = Settings(defaults)
+        reclass = Core(storage, class_mappings, settings)
 
         if options.mode == MODE_NODEINFO:
             data = reclass.nodeinfo(options.nodename)
-
         else:
             data = reclass.inventory()
 
-        print output(data, options.output, options.pretty_print)
+        print(output(data, options.output, options.pretty_print, options.no_refs))
 
-    except ReclassException, e:
+    except ReclassException as e:
         e.exit_with_message(sys.stderr)
 
     sys.exit(posix.EX_OK)
diff --git a/reclass/config.py b/reclass/config.py
index 17d0dc6..e9bb43b 100644
--- a/reclass/config.py
+++ b/reclass/config.py
@@ -12,6 +12,7 @@
 import errors
 from defaults import *
 from constants import MODE_NODEINFO, MODE_INVENTORY
+from reclass import get_path_mangler
 
 def make_db_options_group(parser, defaults={}):
     ret = optparse.OptionGroup(parser, 'Database options',
@@ -20,15 +21,20 @@
                    default=defaults.get('storage_type', OPT_STORAGE_TYPE),
                    help='the type of storage backend to use [%default]')
     ret.add_option('-b', '--inventory-base-uri', dest='inventory_base_uri',
-                   default=defaults.get('inventory_base_uri',
-                                        OPT_INVENTORY_BASE_URI),
+                   default=defaults.get('inventory_base_uri', OPT_INVENTORY_BASE_URI),
                    help='the base URI to prepend to nodes and classes [%default]'),
     ret.add_option('-u', '--nodes-uri', dest='nodes_uri',
                    default=defaults.get('nodes_uri', OPT_NODES_URI),
                    help='the URI to the nodes storage [%default]'),
     ret.add_option('-c', '--classes-uri', dest='classes_uri',
                    default=defaults.get('classes_uri', OPT_CLASSES_URI),
-                   help='the URI to the classes storage [%default]')
+                   help='the URI to the classes storage [%default]'),
+    ret.add_option('-z', '--ignore-class-notfound', dest='ignore_class_notfound',
+                   default=defaults.get('ignore_class_notfound', OPT_IGNORE_CLASS_NOTFOUND),
+                   help='decision for not found classes [%default]')
+    ret.add_option('-x', '--ignore-class-notfound-regexp', dest='ignore_class_notfound_regexp',
+                   default=defaults.get('ignore_class_notfound_regexp', OPT_IGNORE_CLASS_NOTFOUND_REGEXP),
+                   help='regexp for not found classes [%default]')
     return ret
 
 
@@ -38,10 +44,17 @@
     ret.add_option('-o', '--output', dest='output',
                    default=defaults.get('output', OPT_OUTPUT),
                    help='output format (yaml or json) [%default]')
-    ret.add_option('-y', '--pretty-print', dest='pretty_print',
-                   action="store_true",
+    ret.add_option('-y', '--pretty-print', dest='pretty_print', action="store_true",
                    default=defaults.get('pretty_print', OPT_PRETTY_PRINT),
                    help='try to make the output prettier [%default]')
+    ret.add_option('-r', '--no-refs', dest='no_refs', action="store_true",
+                   default=defaults.get('no_refs', OPT_NO_REFS),
+                   help='output all key values do not use yaml references [%default]')
+    ret.add_option('-1', '--single-error', dest='group_errors', action="store_false",
+                   default=defaults.get('group_errors', OPT_GROUP_ERRORS),
+                   help='throw errors immediately instead of grouping them together')
+    ret.add_option('-0', '--multiple-errors', dest='group_errors', action="store_true",
+                   help='were possible report any errors encountered as a group')
     return ret
 
 
@@ -128,30 +141,6 @@
     return parser, option_checker
 
 
-def path_mangler(inventory_base_uri, nodes_uri, classes_uri):
-
-    if inventory_base_uri is None:
-        # if inventory_base is not given, default to current directory
-        inventory_base_uri = os.getcwd()
-
-    nodes_uri = nodes_uri or 'nodes'
-    classes_uri = classes_uri or 'classes'
-
-    def _path_mangler_inner(path):
-        ret = os.path.join(inventory_base_uri, path)
-        ret = os.path.expanduser(ret)
-        return os.path.abspath(ret)
-
-    n, c = map(_path_mangler_inner, (nodes_uri, classes_uri))
-    if n == c:
-        raise errors.DuplicateUriError(n, c)
-    common = os.path.commonprefix((n, c))
-    if common == n or common == c:
-        raise errors.UriOverlapError(n, c)
-
-    return n, c
-
-
 def get_options(name, version, description,
                             inventory_shortopt='-i',
                             inventory_longopt='--inventory',
@@ -175,9 +164,8 @@
     options, args = parser.parse_args()
     checker(options, args)
 
-    options.nodes_uri, options.classes_uri = \
-            path_mangler(options.inventory_base_uri, options.nodes_uri,
-                         options.classes_uri)
+    path_mangler = get_path_mangler(options.storage_type)
+    options.nodes_uri, options.classes_uri = path_mangler(options.inventory_base_uri, options.nodes_uri, options.classes_uri)
 
     return options
 
diff --git a/reclass/core.py b/reclass/core.py
index 76bd0a8..1a08db8 100644
--- a/reclass/core.py
+++ b/reclass/core.py
@@ -7,21 +7,39 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 
+import copy
 import time
-#import types
 import re
-#import sys
 import fnmatch
 import shlex
-from reclass.datatypes import Entity, Classes, Parameters
-from reclass.errors import MappingFormatError, ClassNotFound
+import string
+import sys
+import yaml
+
+from six import iteritems
+
+from reclass.settings import Settings
+from reclass.output.yaml_outputter import ExplicitDumper
+from reclass.datatypes import Entity, Classes, Parameters, Exports
+from reclass.errors import MappingFormatError, ClassNameResolveError, ClassNotFound, InvQueryClassNameResolveError, InvQueryClassNotFound, InvQueryError, InterpolationError, ResolveError
+from reclass.values.parser import Parser
+
+try:
+    basestring
+except NameError:
+    basestring = str
 
 class Core(object):
 
-    def __init__(self, storage, class_mappings, input_data=None):
+    _parser = Parser()
+
+    def __init__(self, storage, class_mappings, settings, input_data=None):
         self._storage = storage
         self._class_mappings = class_mappings
+        self._settings = settings
         self._input_data = input_data
+        if self._settings.ignore_class_notfound:
+            self._cnf_r = re.compile('|'.join([x for x in self._settings.ignore_class_notfound_regexp]))
 
     @staticmethod
     def _get_timestamp():
@@ -47,7 +65,7 @@
             regexp = True
         try:
             key = lexer.get_token()
-        except ValueError, e:
+        except ValueError as e:
             raise MappingFormatError('Error in mapping "{0}": missing closing '
                                      'quote (or slash)'.format(instr))
         if regexp:
@@ -56,7 +74,7 @@
 
     def _get_class_mappings_entity(self, nodename):
         if not self._class_mappings:
-            return Entity(name='empty (class mappings)')
+            return Entity(self._settings, name='empty (class mappings)')
         c = Classes()
         for mapping in self._class_mappings:
             matched = False
@@ -72,32 +90,54 @@
                     for klass in klasses:
                         c.append_if_new(klass)
 
-        return Entity(classes=c,
+        return Entity(self._settings, classes=c,
                       name='class mappings for node {0}'.format(nodename))
 
     def _get_input_data_entity(self):
         if not self._input_data:
-            return Entity(name='empty (input data)')
-        p = Parameters(self._input_data)
-        return Entity(parameters=p, name='input data')
+            return Entity(self._settings, name='empty (input data)')
+        p = Parameters(self._input_data, self._settings)
+        return Entity(self._settings, parameters=p, name='input data')
 
-    def _recurse_entity(self, entity, merge_base=None, seen=None, nodename=None):
+    def _recurse_entity(self, entity, merge_base=None, context=None, seen=None, nodename=None, environment=None):
         if seen is None:
             seen = {}
 
+        if environment is None:
+            environment = self._settings.default_environment
+
         if merge_base is None:
-            merge_base = Entity(name='empty (@{0})'.format(nodename))
+            merge_base = Entity(self._settings, name='empty (@{0})'.format(nodename))
+
+        if context is None:
+            context = Entity(self._settings, name='empty (@{0})'.format(nodename))
 
         for klass in entity.classes.as_list():
+            if klass.count('$') > 0:
+                try:
+                    klass = str(self._parser.parse(klass, self._settings).render(merge_base.parameters.as_dict(), {}))
+                except ResolveError as e:
+                    try:
+                        klass = str(self._parser.parse(klass, self._settings).render(context.parameters.as_dict(), {}))
+                    except ResolveError as e:
+                        raise ClassNameResolveError(klass, nodename, entity.uri)
+
             if klass not in seen:
                 try:
-                    class_entity = self._storage.get_class(klass)
-                except ClassNotFound, e:
-                    e.set_nodename(nodename)
-                    raise e
+                    class_entity = self._storage.get_class(klass, environment, self._settings)
+                except ClassNotFound as e:
+                    if self._settings.ignore_class_notfound:
+                        if self._cnf_r.match(klass):
+                            if self._settings.ignore_class_notfound_warning:
+                                # TODO, add logging handler
+                                print >>sys.stderr, "[WARNING] Reclass class not found: '%s'. Skipped!" % klass
+                            continue
+                    e.nodename = nodename
+                    e.uri = entity.uri
+                    raise
 
-                descent = self._recurse_entity(class_entity, seen=seen,
-                                               nodename=nodename)
+                descent = self._recurse_entity(class_entity, context=merge_base, seen=seen,
+                                               nodename=nodename, environment=environment)
                 # on every iteration, we merge the result of the recursive
                 # descent into what we have so far…
                 merge_base.merge(descent)
@@ -109,18 +149,74 @@
         merge_base.merge(entity)
         return merge_base
 
-    def _nodeinfo(self, nodename):
-        node_entity = self._storage.get_node(nodename)
-        base_entity = Entity(name='base')
+    def _get_automatic_parameters(self, nodename, environment):
+        if self._settings.automatic_parameters:
+            return Parameters({ '_reclass_': { 'name': { 'full': nodename, 'short': str.split(nodename, '.')[0] },
+                                               'environment': environment } }, self._settings, '__auto__')
+        else:
+            return Parameters({}, self._settings, '')
+
+    def _get_inventory(self, all_envs, environment, queries):
+        inventory = {}
+        for nodename in self._storage.enumerate_nodes():
+            try:
+                node_base = self._storage.get_node(nodename, self._settings)
+                if node_base.environment == None:
+                    node_base.environment = self._settings.default_environment
+            except yaml.scanner.ScannerError as e:
+                if self._settings.inventory_ignore_failed_node:
+                    continue
+                else:
+                    raise
+
+            if all_envs or node_base.environment == environment:
+                try:
+                    node = self._node_entity(nodename)
+                except ClassNotFound as e:
+                    raise InvQueryClassNotFound(e)
+                except ClassNameResolveError as e:
+                    raise InvQueryClassNameResolveError(e)
+                if queries is None:
+                    try:
+                        node.interpolate_exports()
+                    except InterpolationError as e:
+                        e.nodename = nodename
+                else:
+                    node.initialise_interpolation()
+                    for p, q in queries:
+                        try:
+                            node.interpolate_single_export(q)
+                        except InterpolationError as e:
+                            e.nodename = nodename
+                            raise InvQueryError(q.contents(), e, context=p, uri=q.uri())
+                inventory[nodename] = node.exports.as_dict()
+        return inventory
+
+    def _node_entity(self, nodename):
+        node_entity = self._storage.get_node(nodename, self._settings)
+        if node_entity.environment == None:
+            node_entity.environment = self._settings.default_environment
+        base_entity = Entity(self._settings, name='base')
         base_entity.merge(self._get_class_mappings_entity(node_entity.name))
         base_entity.merge(self._get_input_data_entity())
+        base_entity.merge_parameters(self._get_automatic_parameters(nodename, node_entity.environment))
         seen = {}
-        merge_base = self._recurse_entity(base_entity, seen=seen,
-                                          nodename=base_entity.name)
-        ret = self._recurse_entity(node_entity, merge_base, seen=seen,
-                                   nodename=node_entity.name)
-        ret.interpolate()
-        return ret
+        merge_base = self._recurse_entity(base_entity, seen=seen, nodename=nodename,
+                                          environment=node_entity.environment)
+        return self._recurse_entity(node_entity, merge_base=merge_base, context=merge_base, seen=seen,
+                                    nodename=nodename, environment=node_entity.environment)
+
+    def _nodeinfo(self, nodename, inventory):
+        try:
+            node = self._node_entity(nodename)
+            node.initialise_interpolation()
+            if node.parameters.has_inv_query() and inventory is None:
+                inventory = self._get_inventory(node.parameters.needs_all_envs(), node.environment, node.parameters.get_inv_queries())
+            node.interpolate(inventory)
+            return node
+        except InterpolationError as e:
+            e.nodename = nodename
+            raise
 
     def _nodeinfo_as_dict(self, nodename, entity):
         ret = {'__reclass__' : {'node': entity.name, 'name': nodename,
@@ -133,17 +229,23 @@
         return ret
 
     def nodeinfo(self, nodename):
-        return self._nodeinfo_as_dict(nodename, self._nodeinfo(nodename))
+        return self._nodeinfo_as_dict(nodename, self._nodeinfo(nodename, None))
 
     def inventory(self):
+        query_nodes = set()
         entities = {}
+        inventory = self._get_inventory(True, '', None)
         for n in self._storage.enumerate_nodes():
-            entities[n] = self._nodeinfo(n)
+            entities[n] = self._nodeinfo(n, inventory)
+            if entities[n].parameters.has_inv_query():
+                nodes.add(n)
+        for n in query_nodes:
+            entities[n] = self._nodeinfo(n, inventory)
 
         nodes = {}
         applications = {}
         classes = {}
-        for f, nodeinfo in entities.iteritems():
+        for (f, nodeinfo) in iteritems(entities):
             d = nodes[f] = self._nodeinfo_as_dict(f, nodeinfo)
             for a in d['applications']:
                 if a in applications:
diff --git a/reclass/datatypes/__init__.py b/reclass/datatypes/__init__.py
index 20f7551..48c4a8b 100644
--- a/reclass/datatypes/__init__.py
+++ b/reclass/datatypes/__init__.py
@@ -6,7 +6,8 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
-from applications import Applications
-from classes import Classes
-from entity import Entity
-from parameters import Parameters
+from .applications import Applications
+from .classes import Classes
+from .entity import Entity
+from .exports import Exports
+from .parameters import Parameters
diff --git a/reclass/datatypes/applications.py b/reclass/datatypes/applications.py
index d024e97..3c7afce 100644
--- a/reclass/datatypes/applications.py
+++ b/reclass/datatypes/applications.py
@@ -7,7 +7,7 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 
-from classes import Classes
+from .classes import Classes
 
 class Applications(Classes):
     '''
diff --git a/reclass/datatypes/classes.py b/reclass/datatypes/classes.py
index b8793a2..090ed70 100644
--- a/reclass/datatypes/classes.py
+++ b/reclass/datatypes/classes.py
@@ -7,12 +7,13 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 
-import types
+import six
 import os
 from reclass.errors import InvalidClassnameError
 
 INVALID_CHARACTERS_FOR_CLASSNAMES = ' ' + os.sep
 
+
 class Classes(object):
     '''
     A very limited ordered set of strings with O(n) uniqueness constraints. It
@@ -51,7 +52,7 @@
             self.append_if_new(i)
 
     def _assert_is_string(self, item):
-        if not isinstance(item, types.StringTypes):
+        if not isinstance(item, six.string_types):
             raise TypeError('%s instances can only contain strings, '\
                             'not %s' % (self.__class__.__name__, type(item)))
 
diff --git a/reclass/datatypes/entity.py b/reclass/datatypes/entity.py
index 573a28c..b43ac72 100644
--- a/reclass/datatypes/entity.py
+++ b/reclass/datatypes/entity.py
@@ -6,9 +6,10 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
-from classes import Classes
-from applications import Applications
-from parameters import Parameters
+from .classes import Classes
+from .applications import Applications
+from .exports import Exports
+from .parameters import Parameters
 
 class Entity(object):
     '''
@@ -16,24 +17,35 @@
     for merging. The name and uri of an Entity will be updated to the name and
     uri of the Entity that is being merged.
     '''
-    def __init__(self, classes=None, applications=None, parameters=None,
-                 uri=None, name=None, environment=None):
+    def __init__(self, settings, classes=None, applications=None, parameters=None,
+                 exports=None, uri=None, name=None, environment=None):
+        self._uri = uri or ''
+        self._name = name or ''
         if classes is None: classes = Classes()
         self._set_classes(classes)
         if applications is None: applications = Applications()
         self._set_applications(applications)
-        if parameters is None: parameters = Parameters()
+        if parameters is None: parameters = Parameters(None, settings, uri)
+        if exports is None: exports = Exports(None, settings, uri)
         self._set_parameters(parameters)
-        self._uri = uri or ''
-        self._name = name or ''
-        self._environment = environment or ''
+        self._set_exports(exports)
+        self._environment = environment
 
     name = property(lambda s: s._name)
+    short_name = property(lambda s: s._short_name)
     uri = property(lambda s: s._uri)
-    environment = property(lambda s: s._environment)
     classes = property(lambda s: s._classes)
     applications = property(lambda s: s._applications)
     parameters = property(lambda s: s._parameters)
+    exports = property(lambda s: s._exports)
+
+    @property
+    def environment(self):
+        return self._environment
+
+    @environment.setter
+    def environment(self, value):
+        self._environment = value
 
     def _set_classes(self, classes):
         if not isinstance(classes, Classes):
@@ -53,22 +65,46 @@
                             'instance of type %s' % type(parameters))
         self._parameters = parameters
 
+    def _set_exports(self, exports):
+        if not isinstance(exports, Exports):
+            raise TypeError('Entity.exports cannot be set to '\
+                            'instance of type %s' % type(exports))
+        self._exports = exports
+
     def merge(self, other):
         self._classes.merge_unique(other._classes)
         self._applications.merge_unique(other._applications)
         self._parameters.merge(other._parameters)
+        self._exports.merge(other._exports)
         self._name = other.name
         self._uri = other.uri
-        self._environment = other.environment
+        if other.environment != None:
+            self._environment = other.environment
 
-    def interpolate(self):
-        self._parameters.interpolate()
+    def merge_parameters(self, params):
+        self._parameters.merge(params)
+
+    def interpolate(self, inventory):
+        self._parameters.interpolate(inventory)
+        self.interpolate_exports()
+
+    def initialise_interpolation(self):
+        self._parameters.initialise_interpolation()
+        self._exports.initialise_interpolation()
+
+    def interpolate_exports(self):
+        self.initialise_interpolation()
+        self._exports.interpolate_from_external(self._parameters)
+
+    def interpolate_single_export(self, references):
+        self._exports.interpolate_single_from_external(self._parameters, references)
 
     def __eq__(self, other):
         return isinstance(other, type(self)) \
                 and self._applications == other._applications \
                 and self._classes == other._classes \
                 and self._parameters == other._parameters \
+                and self._exports == other._exports \
                 and self._name == other._name \
                 and self._uri == other._uri
 
@@ -76,16 +112,15 @@
         return not self.__eq__(other)
 
     def __repr__(self):
-        return "%s(%r, %r, %r, uri=%r, name=%r)" % (self.__class__.__name__,
-                                                    self.classes,
-                                                    self.applications,
-                                                    self.parameters,
-                                                    self.uri,
-                                                    self.name)
+        return "%s(%r, %r, %r, %r, uri=%r, name=%r, environment=%r)" % (
+                   self.__class__.__name__, self.classes, self.applications,
+                   self.parameters, self.exports, self.uri, self.name,
+                   self.environment)
 
     def as_dict(self):
         return {'classes': self._classes.as_list(),
                 'applications': self._applications.as_list(),
                 'parameters': self._parameters.as_dict(),
+                'exports': self._exports.as_dict(),
                 'environment': self._environment
                }
diff --git a/reclass/datatypes/exports.py b/reclass/datatypes/exports.py
new file mode 100644
index 0000000..971befa
--- /dev/null
+++ b/reclass/datatypes/exports.py
@@ -0,0 +1,94 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass (http://github.com/madduck/reclass)
+#
+
+import copy
+
+from six import iteritems, next
+
+from .parameters import Parameters
+from reclass.errors import ResolveError
+from reclass.values.value import Value
+from reclass.values.valuelist import ValueList
+from reclass.utils.dictpath import DictPath
+
+class Exports(Parameters):
+
+    def __init__(self, mapping, settings, uri):
+        super(Exports, self).__init__(mapping, settings, uri)
+
+    def __repr__(self):
+        return '%s(%r)' % (self.__class__.__name__, self._base)
+
+    def delete_key(self, key):
+        self._base.pop(key, None)
+        self._unrendered.pop(key, None)
+
+    def overwrite(self, other):
+        overdict = {'~' + key: value for (key, value) in iteritems(other)}
+        self.merge(overdict)
+
+    def interpolate_from_external(self, external):
+        while len(self._unrendered) > 0:
+            path, v = next(iteritems(self._unrendered))
+            value = path.get_value(self._base)
+            if isinstance(value, (Value, ValueList)):
+                external._interpolate_references(path, value, None)
+                new = self._interpolate_render_from_external(external._base, path, value)
+                path.set_value(self._base, new)
+                del self._unrendered[path]
+            else:
+                # references to lists and dicts are only deepcopied when merged
+                # together so it's possible a value with references in a referenced
+                # list or dict has already been rendered
+                del self._unrendered[path]
+
+    def interpolate_single_from_external(self, external, query):
+        for r in query.get_inv_references():
+            self._interpolate_single_path_from_external(r, external, query)
+
+    def _interpolate_single_path_from_external(self, mainpath, external, query):
+        required = self._get_required_paths(mainpath)
+        while len(required) > 0:
+            while len(required) > 0:
+                path, v = next(iteritems(required))
+                value = path.get_value(self._base)
+                if isinstance(value, (Value, ValueList)):
+                    try:
+                        external._interpolate_references(path, value, None)
+                        new = self._interpolate_render_from_external(external._base, path, value)
+                        path.set_value(self._base, new)
+                    except ResolveError as e:
+                        if query.ignore_failed_render():
+                            path.delete(self._base)
+                        else:
+                            raise
+                del required[path]
+                del self._unrendered[path]
+            required = self._get_required_paths(mainpath)
+
+    def _get_required_paths(self, mainpath):
+        paths = {}
+        path = DictPath(self._settings.delimiter)
+        for i in mainpath.key_parts():
+            path.add_subpath(i)
+            if path in self._unrendered:
+                paths[path] = True
+        for i in self._unrendered:
+            if mainpath.is_ancestor_of(i) or mainpath == i:
+                paths[i] = True
+        return paths
+
+    def _interpolate_render_from_external(self, context, path, value):
+        try:
+            new = value.render(context, None)
+        except ResolveError as e:
+            e.context = path
+            raise
+        if isinstance(new, dict):
+            self._render_simple_dict(new, path)
+        elif isinstance(new, list):
+            self._render_simple_list(new, path)
+        return new
diff --git a/reclass/datatypes/parameters.py b/reclass/datatypes/parameters.py
index 37419fc..6ad0d27 100644
--- a/reclass/datatypes/parameters.py
+++ b/reclass/datatypes/parameters.py
@@ -6,12 +6,19 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+
+import copy
+import sys
 import types
 
-from reclass.defaults import PARAMETER_INTERPOLATION_DELIMITER
+from six import iteritems, next
+
+from collections import namedtuple
 from reclass.utils.dictpath import DictPath
-from reclass.utils.refvalue import RefValue
-from reclass.errors import InfiniteRecursionError, UndefinedVariableError
+from reclass.values.value import Value
+from reclass.values.valuelist import ValueList
+from reclass.errors import InfiniteRecursionError, ResolveError, ResolveErrorList, InterpolationError, ParseError, BadReferencesError
+
 
 class Parameters(object):
     '''
@@ -36,185 +43,296 @@
     To support these specialities, this class only exposes very limited
     functionality and does not try to be a really mapping object.
     '''
-    DEFAULT_PATH_DELIMITER = PARAMETER_INTERPOLATION_DELIMITER
 
-    def __init__(self, mapping=None, delimiter=None):
-        if delimiter is None:
-            delimiter = Parameters.DEFAULT_PATH_DELIMITER
-        self._delimiter = delimiter
+    def __init__(self, mapping, settings, uri, parse_strings=True):
+        self._settings = settings
         self._base = {}
-        self._occurrences = {}
+        self._uri = uri
+        self._unrendered = None
+        self._escapes_handled = {}
+        self._inv_queries = []
+        self._resolve_errors = ResolveErrorList()
+        self._needs_all_envs = False
+        self._keep_overrides = False
+        self._parse_strings = parse_strings
         if mapping is not None:
-            # we initialise by merging, otherwise the list of references might
-            # not be updated
+            # we initialise by merging
+            self._keep_overrides = True
             self.merge(mapping)
+            self._keep_overrides = False
 
-    delimiter = property(lambda self: self._delimiter)
+    #delimiter = property(lambda self: self._delimiter)
 
     def __len__(self):
         return len(self._base)
 
     def __repr__(self):
-        return '%s(%r, %r)' % (self.__class__.__name__, self._base,
-                               self.delimiter)
+        return '%s(%r)' % (self.__class__.__name__, self._base)
 
     def __eq__(self, other):
         return isinstance(other, type(self)) \
                 and self._base == other._base \
-                and self._delimiter == other._delimiter
+                and self._settings == other._settings
 
     def __ne__(self, other):
         return not self.__eq__(other)
 
+    def has_inv_query(self):
+        return len(self._inv_queries) > 0
+
+    def get_inv_queries(self):
+        return self._inv_queries
+
+    def needs_all_envs(self):
+        return self._needs_all_envs
+
+    def resolve_errors(self):
+        return self._resolve_errors
+
     def as_dict(self):
         return self._base.copy()
 
-    def _update_scalar(self, cur, new, path):
-        if isinstance(cur, RefValue) and path in self._occurrences:
-            # If the current value already holds a RefValue, we better forget
-            # the occurrence, or else interpolate() will later overwrite
-            # unconditionally. If the new value is a RefValue, the occurrence
-            # will be added again further on
-            del self._occurrences[path]
-
-        if self.delimiter is None or not isinstance(new, (types.StringTypes,
-                                                          RefValue)):
-            # either there is no delimiter defined (and hence no references
-            # are being used), or the new value is not a string (and hence
-            # cannot be turned into a RefValue), and not a RefValue. We can
-            # shortcut and just return the new scalar
-            return new
-
-        elif isinstance(new, RefValue):
-            # the new value is (already) a RefValue, so we need not touch it
-            # at all
-            ret = new
-
+    def _wrap_value(self, value, path):
+        if isinstance(value, dict):
+            return self._wrap_dict(value, path)
+        elif isinstance(value, list):
+            return self._wrap_list(value, path)
+        elif isinstance(value, (Value, ValueList)):
+            return value
         else:
-            # the new value is a string, let's see if it contains references,
-            # by way of wrapping it in a RefValue and querying the result
-            ret = RefValue(new, self.delimiter)
-            if not ret.has_references():
-                # do not replace with RefValue instance if there are no
-                # references, i.e. discard the RefValue in ret, just return
-                # the new value
-                return new
+            try:
+                return Value(value, self._settings, self._uri, parse_string=self._parse_strings)
+            except InterpolationError as e:
+                e.context = str(path)
+                raise
 
-        # So we now have a RefValue. Let's, keep a reference to the instance
-        # we just created, in a dict indexed by the dictionary path, instead
-        # of just a list. The keys are required to resolve dependencies during
-        # interpolation
-        self._occurrences[path] = ret
-        return ret
+    def _wrap_list(self, source, path):
+        return [ self._wrap_value(v, path.new_subpath(k)) for (k, v) in enumerate(source) ]
 
-    def _extend_list(self, cur, new, path):
-        if isinstance(cur, list):
-            ret = cur
-            offset = len(cur)
+    def _wrap_dict(self, source, path):
+        return { k: self._wrap_value(v, path.new_subpath(k)) for (k, v) in iteritems(source) }
+
+    def _update_value(self, cur, new):
+        if isinstance(cur, Value):
+            values = ValueList(cur, self._settings)
+        elif isinstance(cur, ValueList):
+            values = cur
         else:
-            ret = [cur]
-            offset = 1
+            values = ValueList(Value(cur, self._settings, self._uri), self._settings)
 
-        for i in xrange(len(new)):
-            ret.append(self._merge_recurse(None, new[i], path.new_subpath(offset + i)))
-        return ret
+        if isinstance(new, Value):
+            values.append(new)
+        elif isinstance(new, ValueList):
+            values.extend(new)
+        else:
+            values.append(Value(new, self._settings, self._uri, parse_string=self._parse_strings))
+
+        return values
 
     def _merge_dict(self, cur, new, path):
-        if isinstance(cur, dict):
-            ret = cur
-        else:
-            # nothing sensible to do
-            raise TypeError('Cannot merge dict into {0} '
-                            'objects'.format(type(cur)))
+        """Merge a dictionary with another dictionary.
 
-        if self.delimiter is None:
-            # a delimiter of None indicates that there is no value
-            # processing to be done, and since there is no current
-            # value, we do not need to walk the new dictionary:
-            ret.update(new)
-            return ret
+        Iterate over keys in new. If this is not an initialization merge and
+        the key begins with PARAMETER_DICT_KEY_OVERRIDE_PREFIX, override the
+        value of the key in cur. Otherwise deeply merge the contents of the key
+        in cur with the contents of the key in _merge_recurse over the item.
 
-        for key, newvalue in new.iteritems():
-            ret[key] = self._merge_recurse(ret.get(key), newvalue,
-                                           path.new_subpath(key))
+        Args:
+            cur (dict): Current dictionary
+            new (dict): Dictionary to be merged
+            path (string): Merging path from recursion
+            initmerge (bool): True if called as part of entity init
+
+        Returns:
+            dict: a merged dictionary
+
+        """
+
+        ret = cur
+        for (key, newvalue) in iteritems(new):
+            if key.startswith(self._settings.dict_key_override_prefix) and not self._keep_overrides:
+                if not isinstance(newvalue, Value):
+                    newvalue = Value(newvalue, self._settings, self._uri, parse_string=self._parse_strings)
+                newvalue.overwrite = True
+                ret[key.lstrip(self._settings.dict_key_override_prefix)] = newvalue
+            else:
+                ret[key] = self._merge_recurse(ret.get(key), newvalue, path.new_subpath(key))
         return ret
 
     def _merge_recurse(self, cur, new, path=None):
-        if path is None:
-            path = DictPath(self.delimiter)
+        """Merge a parameter with another parameter.
 
-        if isinstance(new, dict):
-            if cur is None:
-                cur = {}
+        Iterate over keys in new. Call _merge_dict, _extend_list, or
+        _update_scalar depending on type. Pass along whether this is an
+        initialization merge.
+
+        Args:
+            cur (dict): Current dictionary
+            new (dict): Dictionary to be merged
+            path (string): Merging path from recursion
+            initmerge (bool): True if called as part of entity init, defaults
+                to False
+
+        Returns:
+            dict: a merged dictionary
+
+        """
+
+        if cur is None:
+            return new
+        elif isinstance(new, dict) and isinstance(cur, dict):
             return self._merge_dict(cur, new, path)
-
-        elif isinstance(new, list):
-            if cur is None:
-                cur = []
-            return self._extend_list(cur, new, path)
-
         else:
-            return self._update_scalar(cur, new, path)
+            return self._update_value(cur, new)
 
     def merge(self, other):
+        """Merge function (public edition).
+
+        Call _merge_recurse on self with either another Parameter object or a
+        dict (for initialization). Set initmerge if it's a dict.
+
+        Args:
+            other (dict or Parameter): Thing to merge with self._base
+
+        Returns:
+            None: Nothing
+
+        """
+
+        self._unrendered = None
         if isinstance(other, dict):
-            self._base = self._merge_recurse(self._base, other, None)
-
+            wrapped = self._wrap_dict(other, DictPath(self._settings.delimiter))
         elif isinstance(other, self.__class__):
-            self._base = self._merge_recurse(self._base, other._base,
-                                             None)
-
+            wrapped = self._wrap_dict(other._base, DictPath(self._settings.delimiter))
         else:
             raise TypeError('Cannot merge %s objects into %s' % (type(other),
                             self.__class__.__name__))
+        self._base = self._merge_recurse(self._base, wrapped, DictPath(self._settings.delimiter))
 
-    def has_unresolved_refs(self):
-        return len(self._occurrences) > 0
+    def _render_simple_container(self, container, key, value, path):
+            if isinstance(value, ValueList):
+                if value.is_complex():
+                    p = path.new_subpath(key)
+                    self._unrendered[p] = True
+                    if value.has_inv_query():
+                        self._inv_queries.append((p, value))
+                        if value.needs_all_envs():
+                            self._needs_all_envs = True
+                    return
+                else:
+                    value = value.merge()
+            if isinstance(value, Value) and value.is_container():
+                value = value.contents()
+            if isinstance(value, dict):
+                self._render_simple_dict(value, path.new_subpath(key))
+                container[key] = value
+            elif isinstance(value, list):
+                self._render_simple_list(value, path.new_subpath(key))
+                container[key] = value
+            elif isinstance(value, Value):
+                if value.is_complex():
+                    p = path.new_subpath(key)
+                    self._unrendered[p] = True
+                    if value.has_inv_query():
+                        self._inv_queries.append((p, value))
+                        if value.needs_all_envs():
+                            self._needs_all_envs = True
+                else:
+                    container[key] = value.render(None, None)
 
-    def interpolate(self):
-        while self.has_unresolved_refs():
+    def _render_simple_dict(self, dictionary, path):
+        for (key, value) in iteritems(dictionary):
+            self._render_simple_container(dictionary, key, value, path)
+
+    def _render_simple_list(self, item_list, path):
+        for n, value in enumerate(item_list):
+            self._render_simple_container(item_list, n, value, path)
+
+    def interpolate(self, inventory=None):
+        self._initialise_interpolate()
+        while len(self._unrendered) > 0:
             # we could use a view here, but this is simple enough:
             # _interpolate_inner removes references from the refs hash after
             # processing them, so we cannot just iterate the dict
-            path, refvalue = self._occurrences.iteritems().next()
-            self._interpolate_inner(path, refvalue)
+            path, v = next(iteritems(self._unrendered))
+            self._interpolate_inner(path, inventory)
+        if self._resolve_errors.have_errors():
+            raise self._resolve_errors
 
-    def _interpolate_inner(self, path, refvalue):
-        self._occurrences[path] = True  # mark as seen
-        for ref in refvalue.get_references():
-            path_from_ref = DictPath(self.delimiter, ref)
-            try:
-                refvalue_inner = self._occurrences[path_from_ref]
+    def initialise_interpolation(self):
+        self._unrendered = None
+        self._initialise_interpolate()
 
-                # If there is no reference, then this will throw a KeyError,
-                # look further down where this is caught and execution passed
-                # to the next iteration of the loop
-                #
-                # If we get here, then the ref references another parameter,
-                # requiring us to recurse, dereferencing first those refs that
-                # are most used and are thus at the leaves of the dependency
-                # tree.
+    def _initialise_interpolate(self):
+        if self._unrendered is None:
+            self._unrendered = {}
+            self._inv_queries = []
+            self._needs_all_envs = False
+            self._resolve_errors = ResolveErrorList()
+            self._render_simple_dict(self._base, DictPath(self._settings.delimiter))
 
-                if refvalue_inner is True:
-                    # every call to _interpolate_inner replaces the value of
-                    # the saved occurrences of a reference with True.
-                    # Therefore, if we encounter True instead of a refvalue,
-                    # it means that we have already processed it and are now
-                    # faced with a cyclical reference.
-                    raise InfiniteRecursionError(path, ref)
-                self._interpolate_inner(path_from_ref, refvalue_inner)
+    def _interpolate_inner(self, path, inventory):
+        value = path.get_value(self._base)
+        if not isinstance(value, (Value, ValueList)):
+            # references to lists and dicts are only deepcopied when merged
+            # together so it's possible a value with references in a referenced
+            # list or dict has already been visited by _interpolate_inner
+            del self._unrendered[path]
+            return
+        self._unrendered[path] = False
+        self._interpolate_references(path, value, inventory)
+        new = self._interpolate_render_value(path, value, inventory)
+        path.set_value(self._base, new)
+        del self._unrendered[path]
 
-            except KeyError as e:
-                # not actually an error, but we are done resolving all
-                # dependencies of the current ref, so move on
-                continue
-
+    def _interpolate_render_value(self, path, value, inventory):
         try:
-            new = refvalue.render(self._base)
-            path.set_value(self._base, new)
+            new = value.render(self._base, inventory)
+        except ResolveError as e:
+            e.context = path
+            if self._settings.group_errors:
+                self._resolve_errors.add(e)
+                new = None
+            else:
+                raise
 
-            # finally, remove the reference from the occurrences cache
-            del self._occurrences[path]
-        except UndefinedVariableError as e:
-            raise UndefinedVariableError(e.var, path)
+        if isinstance(new, dict):
+            self._render_simple_dict(new, path)
+        elif isinstance(new, list):
+            self._render_simple_list(new, path)
+        return new
 
+    def _interpolate_references(self, path, value, inventory):
+        all_refs = False
+        while not all_refs:
+            for ref in value.get_references():
+                path_from_ref = DictPath(self._settings.delimiter, ref)
+
+                if path_from_ref in self._unrendered:
+                    if self._unrendered[path_from_ref] is False:
+                        # every call to _interpolate_inner replaces the value of
+                        # self._unrendered[path] with False
+                        # Therefore, if we encounter False instead of True,
+                        # it means that we have already processed it and are now
+                        # faced with a cyclical reference.
+                        raise InfiniteRecursionError(path, ref, value.uri())
+                    else:
+                        self._interpolate_inner(path_from_ref, inventory)
+                else:
+                    # ensure ancestor keys are already dereferenced
+                    ancestor = DictPath(self._settings.delimiter)
+                    for k in path_from_ref.key_parts():
+                        ancestor = ancestor.new_subpath(k)
+                        if ancestor in self._unrendered:
+                            self._interpolate_inner(ancestor, inventory)
+            if value.allRefs():
+                all_refs = True
+            else:
+                # not all references in the value could be calculated previously so
+                # try recalculating references with current context and recursively
+                # call _interpolate_inner if the number of references has increased
+                # Otherwise raise an error
+                old = len(value.get_references())
+                value.assembleRefs(self._base)
+                if old == len(value.get_references()):
+                    raise BadReferencesError(value.get_references(), str(path), value.uri())
diff --git a/reclass/datatypes/tests/test_applications.py b/reclass/datatypes/tests/test_applications.py
index 307a430..6ae07cc 100644
--- a/reclass/datatypes/tests/test_applications.py
+++ b/reclass/datatypes/tests/test_applications.py
@@ -63,7 +63,7 @@
         l = ['a', '~b', 'a', '~d']
         a = Applications(l)
         is_negation = lambda x: x.startswith(a.negation_prefix)
-        GOAL = filter(lambda x: not is_negation(x), set(l)) + filter(is_negation, l)
+        GOAL = list(filter(lambda x: not is_negation(x), set(l))) + list(filter(is_negation, l))
         self.assertEqual('%r' % a, "%s(%r, '~')" % (a.__class__.__name__, GOAL))
 
 if __name__ == '__main__':
diff --git a/reclass/datatypes/tests/test_entity.py b/reclass/datatypes/tests/test_entity.py
index 17ec9e8..f398d51 100644
--- a/reclass/datatypes/tests/test_entity.py
+++ b/reclass/datatypes/tests/test_entity.py
@@ -6,91 +6,99 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
-from reclass.datatypes import Entity, Classes, Parameters, Applications
+
+from reclass.settings import Settings
+from reclass.datatypes import Entity, Classes, Parameters, Applications, Exports
+from reclass.errors import ResolveError
 import unittest
 try:
     import unittest.mock as mock
 except ImportError:
     import mock
 
+SETTINGS = Settings()
+
 @mock.patch.multiple('reclass.datatypes', autospec=True, Classes=mock.DEFAULT,
-                     Applications=mock.DEFAULT,
-                     Parameters=mock.DEFAULT)
+                     Applications=mock.DEFAULT, Parameters=mock.DEFAULT,
+                     Exports=mock.DEFAULT)
 class TestEntity(unittest.TestCase):
 
-    def _make_instances(self, Classes, Applications, Parameters):
-        return Classes(), Applications(), Parameters()
+    def _make_instances(self, Classes, Applications, Parameters, Exports):
+        return Classes(), Applications(), Parameters({}, SETTINGS, ""), Exports({}, SETTINGS, "")
 
     def test_constructor_default(self, **mocks):
         # Actually test the real objects by calling the default constructor,
         # all other tests shall pass instances to the constructor
-        e = Entity()
+        e = Entity(SETTINGS)
         self.assertEqual(e.name, '')
         self.assertEqual(e.uri, '')
         self.assertIsInstance(e.classes, Classes)
         self.assertIsInstance(e.applications, Applications)
         self.assertIsInstance(e.parameters, Parameters)
+        self.assertIsInstance(e.exports, Exports)
 
     def test_constructor_empty(self, **types):
         instances = self._make_instances(**types)
-        e = Entity(*instances)
+        e = Entity(SETTINGS, *instances)
         self.assertEqual(e.name, '')
         self.assertEqual(e.uri, '')
-        cl, al, pl = [getattr(i, '__len__') for i in instances]
+        cl, al, pl, ex = [getattr(i, '__len__') for i in instances]
         self.assertEqual(len(e.classes), cl.return_value)
         cl.assert_called_once_with()
         self.assertEqual(len(e.applications), al.return_value)
         al.assert_called_once_with()
         self.assertEqual(len(e.parameters), pl.return_value)
         pl.assert_called_once_with()
+        self.assertEqual(len(e.exports), pl.return_value)
+        ex.assert_called_once_with()
 
     def test_constructor_empty_named(self, **types):
         name = 'empty'
-        e = Entity(*self._make_instances(**types), name=name)
+        e = Entity(SETTINGS, *self._make_instances(**types), name=name)
         self.assertEqual(e.name, name)
 
     def test_constructor_empty_uri(self, **types):
         uri = 'test://uri'
-        e = Entity(*self._make_instances(**types), uri=uri)
+        e = Entity(SETTINGS, *self._make_instances(**types), uri=uri)
         self.assertEqual(e.uri, uri)
 
     def test_constructor_empty_env(self, **types):
         env = 'not base'
-        e = Entity(*self._make_instances(**types), environment=env)
+        e = Entity(SETTINGS, *self._make_instances(**types), environment=env)
         self.assertEqual(e.environment, env)
 
     def test_equal_empty(self, **types):
         instances = self._make_instances(**types)
-        self.assertEqual(Entity(*instances), Entity(*instances))
+        self.assertEqual(Entity(SETTINGS, *instances), Entity(SETTINGS, *instances))
         for i in instances:
             i.__eq__.assert_called_once_with(i)
 
     def test_equal_empty_named(self, **types):
         instances = self._make_instances(**types)
-        self.assertEqual(Entity(*instances), Entity(*instances))
+        self.assertEqual(Entity(SETTINGS, *instances), Entity(SETTINGS, *instances))
         name = 'empty'
-        self.assertEqual(Entity(*instances, name=name),
-                         Entity(*instances, name=name))
+        self.assertEqual(Entity(SETTINGS, *instances, name=name),
+                         Entity(SETTINGS, *instances, name=name))
 
     def test_unequal_empty_uri(self, **types):
         instances = self._make_instances(**types)
         uri = 'test://uri'
-        self.assertNotEqual(Entity(*instances, uri=uri),
-                            Entity(*instances, uri=uri[::-1]))
+        self.assertNotEqual(Entity(SETTINGS, *instances, uri=uri),
+                            Entity(SETTINGS, *instances, uri=uri[::-1]))
         for i in instances:
             i.__eq__.assert_called_once_with(i)
 
     def test_unequal_empty_named(self, **types):
         instances = self._make_instances(**types)
         name = 'empty'
-        self.assertNotEqual(Entity(*instances, name=name),
-                            Entity(*instances, name=name[::-1]))
+        self.assertNotEqual(Entity(SETTINGS, *instances, name=name),
+                            Entity(SETTINGS, *instances, name=name[::-1]))
         for i in instances:
             i.__eq__.assert_called_once_with(i)
 
     def test_unequal_types(self, **types):
         instances = self._make_instances(**types)
-        self.assertNotEqual(Entity(*instances, name='empty'),
+        self.assertNotEqual(Entity(SETTINGS, *instances, name='empty'),
                             None)
         for i in instances:
             self.assertEqual(i.__eq__.call_count, 0)
@@ -98,7 +106,7 @@
     def _test_constructor_wrong_types(self, which_replace, **types):
         instances = self._make_instances(**types)
         instances[which_replace] = 'Invalid type'
-        e = Entity(*instances)
+        e = Entity(SETTINGS, *instances)
 
     def test_constructor_wrong_type_classes(self, **types):
         self.assertRaises(TypeError, self._test_constructor_wrong_types, 0)
@@ -111,7 +119,7 @@
 
     def test_merge(self, **types):
         instances = self._make_instances(**types)
-        e = Entity(*instances)
+        e = Entity(SETTINGS, *instances)
         e.merge(e)
         for i, fn in zip(instances, ('merge_unique', 'merge_unique', 'merge')):
             getattr(i, fn).assert_called_once_with(i)
@@ -119,38 +127,153 @@
     def test_merge_newname(self, **types):
         instances = self._make_instances(**types)
         newname = 'newname'
-        e1 = Entity(*instances, name='oldname')
-        e2 = Entity(*instances, name=newname)
+        e1 = Entity(SETTINGS, *instances, name='oldname')
+        e2 = Entity(SETTINGS, *instances, name=newname)
         e1.merge(e2)
         self.assertEqual(e1.name, newname)
 
     def test_merge_newuri(self, **types):
         instances = self._make_instances(**types)
         newuri = 'test://uri2'
-        e1 = Entity(*instances, uri='test://uri1')
-        e2 = Entity(*instances, uri=newuri)
+        e1 = Entity(SETTINGS, *instances, uri='test://uri1')
+        e2 = Entity(SETTINGS, *instances, uri=newuri)
         e1.merge(e2)
         self.assertEqual(e1.uri, newuri)
 
     def test_merge_newenv(self, **types):
         instances = self._make_instances(**types)
         newenv = 'new env'
-        e1 = Entity(*instances, environment='env')
-        e2 = Entity(*instances, environment=newenv)
+        e1 = Entity(SETTINGS, *instances, environment='env')
+        e2 = Entity(SETTINGS, *instances, environment=newenv)
         e1.merge(e2)
         self.assertEqual(e1.environment, newenv)
 
     def test_as_dict(self, **types):
         instances = self._make_instances(**types)
-        entity = Entity(*instances, name='test', environment='test')
+        entity = Entity(SETTINGS, *instances, name='test', environment='test')
         comp = {}
         comp['classes'] = instances[0].as_list()
         comp['applications'] = instances[1].as_list()
         comp['parameters'] = instances[2].as_dict()
+        comp['exports'] = instances[3].as_dict()
         comp['environment'] = 'test'
         d = entity.as_dict()
         self.assertDictEqual(d, comp)
 
+class TestEntityNoMock(unittest.TestCase):
+
+    def test_exports_with_refs(self):
+        inventory = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 4}}
+        node3_exports = Exports({'a': '${a}', 'b': '${b}'}, SETTINGS, '')
+        node3_parameters = Parameters({'name': 'node3', 'a': '${c}', 'b': 5}, SETTINGS, '')
+        node3_parameters.merge({'c': 3})
+        node3_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node3_parameters, exports=node3_exports)
+        node3_entity.interpolate_exports()
+        inventory['node3'] = node3_entity.exports.as_dict()
+        r = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 4}, 'node3': {'a': 3, 'b': 5}}
+        self.assertDictEqual(inventory, r)
+
+    def test_reference_to_an_export(self):
+        inventory = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 4}}
+        node3_exports = Exports({'a': '${a}', 'b': '${b}'}, SETTINGS, '')
+        node3_parameters = Parameters({'name': 'node3', 'ref': '${exp}', 'a': '${c}', 'b': 5}, SETTINGS, '')
+        node3_parameters.merge({'c': 3, 'exp': '$[ exports:a ]'})
+        node3_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node3_parameters, exports=node3_exports)
+        node3_entity.interpolate_exports()
+        inventory['node3'] = node3_entity.exports.as_dict()
+        node3_entity.interpolate(inventory)
+        res_inv = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 4}, 'node3': {'a': 3, 'b': 5}}
+        res_params = {'a': 3, 'c': 3, 'b': 5, 'name': 'node3', 'exp': {'node1': 1, 'node3': 3, 'node2': 3}, 'ref': {'node1': 1, 'node3': 3, 'node2': 3}}
+        self.assertDictEqual(node3_parameters.as_dict(), res_params)
+        self.assertDictEqual(inventory, res_inv)
+
+    def test_exports_multiple_nodes(self):
+        node1_exports = Exports({'a': '${a}'}, SETTINGS, '')
+        node1_parameters = Parameters({'name': 'node1', 'a': { 'test': '${b}' }, 'b': 1, 'exp': '$[ exports:a ]'}, SETTINGS, '')
+        node1_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node1_parameters, exports=node1_exports)
+        node2_exports = Exports({'a': '${a}'}, SETTINGS, '')
+        node2_parameters = Parameters({'name': 'node2', 'a': { 'test': '${b}' }, 'b': 2 }, SETTINGS, '')
+        node2_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node2_parameters, exports=node2_exports)
+        node1_entity.initialise_interpolation()
+        node2_entity.initialise_interpolation()
+        queries = node1_entity.parameters.get_inv_queries()
+        for p, q in queries:
+            node1_entity.interpolate_single_export(q)
+            node2_entity.interpolate_single_export(q)
+        res_inv = {'node1': {'a': {'test': 1}}, 'node2': {'a': {'test': 2}}}
+        res_params = {'a': {'test': 1}, 'b': 1, 'name': 'node1', 'exp': {'node1': {'test': 1}, 'node2': {'test': 2}}}
+        inventory = {}
+        inventory['node1'] = node1_entity.exports.as_dict()
+        inventory['node2'] = node2_entity.exports.as_dict()
+        node1_entity.interpolate(inventory)
+        self.assertDictEqual(node1_parameters.as_dict(), res_params)
+        self.assertDictEqual(inventory, res_inv)
+
+    def test_exports_with_ancestor_references(self):
+        inventory = {'node1': {'alpha' : {'beta': {'a': 1, 'b': 2}}}, 'node2': {'alpha' : {'beta': {'a': 3, 'b': 4}}}}
+        node3_exports = Exports({'alpha': '${alpha}'}, SETTINGS, '')
+        node3_parameters = Parameters({'name': 'node3', 'alpha': {'beta' : {'a': 5, 'b': 6}}, 'exp': '$[ exports:alpha:beta ]'}, SETTINGS, '')
+        node3_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node3_parameters, exports=node3_exports)
+        res_params = {'exp': {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 4}, 'node3': {'a': 5, 'b': 6}}, 'name': 'node3', 'alpha': {'beta': {'a': 5, 'b': 6}}}
+        res_inv = {'node1': {'alpha' : {'beta': {'a': 1, 'b': 2}}}, 'node2': {'alpha' : {'beta': {'a': 3, 'b': 4}}}, 'node3': {'alpha' : {'beta': {'a': 5, 'b': 6}}}}
+        node3_entity.initialise_interpolation()
+        queries = node3_entity.parameters.get_inv_queries()
+        for p, q in queries:
+            node3_entity.interpolate_single_export(q)
+        inventory['node3'] = node3_entity.exports.as_dict()
+        node3_entity.interpolate(inventory)
+        self.assertDictEqual(node3_parameters.as_dict(), res_params)
+        self.assertDictEqual(inventory, res_inv)
+
+    def test_exports_with_nested_references(self):
+        inventory = {'node1': {'alpha': {'a': 1, 'b': 2}}, 'node2': {'alpha': {'a': 3, 'b': 4}}}
+        node3_exports = Exports({'alpha': '${alpha}'}, SETTINGS, '')
+        node3_parameters = Parameters({'name': 'node3', 'alpha': {'a': '${one}', 'b': '${two}'}, 'beta': '$[ exports:alpha ]', 'one': '111', 'two': '${three}', 'three': '123'}, SETTINGS, '')
+        node3_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node3_parameters, exports=node3_exports)
+        res_params = {'beta': {'node1': {'a': 1, 'b': 2}, 'node3': {'a': '111', 'b': '123'}, 'node2': {'a': 3, 'b': 4}}, 'name': 'node3', 'alpha': {'a': '111', 'b': '123'}, 'three': '123', 'two': '123', 'one': '111'}
+        res_inv = {'node1': {'alpha': {'a': 1, 'b': 2}}, 'node2': {'alpha': {'a': 3, 'b': 4}}, 'node3': {'alpha': {'a': '111', 'b': '123'}}}
+        node3_entity.interpolate_exports()
+        inventory['node3'] = node3_entity.exports.as_dict()
+        node3_entity.interpolate(inventory)
+        self.assertDictEqual(node3_parameters.as_dict(), res_params)
+        self.assertDictEqual(inventory, res_inv)
+
+    def test_exports_failed_render(self):
+        node1_exports = Exports({'a': '${a}'}, SETTINGS, '')
+        node1_parameters = Parameters({'name': 'node1', 'a': 1, 'exp': '$[ exports:a ]'}, SETTINGS, '')
+        node1_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node1_parameters, exports=node1_exports)
+        node2_exports = Exports({'a': '${b}'}, SETTINGS, '')
+        node2_parameters = Parameters({'name': 'node2', 'a': 2}, SETTINGS, '')
+        node2_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node2_parameters, exports=node2_exports)
+        node1_entity.initialise_interpolation()
+        node2_entity.initialise_interpolation()
+        queries = node1_entity.parameters.get_inv_queries()
+        with self.assertRaises(ResolveError):
+            for p, q in queries:
+                node1_entity.interpolate_single_export(q)
+                node2_entity.interpolate_single_export(q)
+
+    def test_exports_failed_render_ignore(self):
+        node1_exports = Exports({'a': '${a}'}, SETTINGS, '')
+        node1_parameters = Parameters({'name': 'node1', 'a': 1, 'exp': '$[ +IgnoreErrors exports:a ]'}, SETTINGS, '')
+        node1_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node1_parameters, exports=node1_exports)
+        node2_exports = Exports({'a': '${b}'}, SETTINGS, '')
+        node2_parameters = Parameters({'name': 'node1', 'a': 2}, SETTINGS, '')
+        node2_entity = Entity(SETTINGS, classes=None, applications=None, parameters=node2_parameters, exports=node2_exports)
+        node1_entity.initialise_interpolation()
+        node2_entity.initialise_interpolation()
+        queries = node1_entity.parameters.get_inv_queries()
+        for p, q in queries:
+            node1_entity.interpolate_single_export(q)
+            node2_entity.interpolate_single_export(q)
+        res_inv = {'node1': {'a': 1}, 'node2': {}}
+        res_params = { 'a': 1, 'name': 'node1', 'exp': {'node1': 1} }
+        inventory = {}
+        inventory['node1'] = node1_entity.exports.as_dict()
+        inventory['node2'] = node2_entity.exports.as_dict()
+        node1_entity.interpolate(inventory)
+        self.assertDictEqual(node1_parameters.as_dict(), res_params)
+        self.assertDictEqual(inventory, res_inv)
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/reclass/datatypes/tests/test_exports.py b/reclass/datatypes/tests/test_exports.py
new file mode 100644
index 0000000..33eccbe
--- /dev/null
+++ b/reclass/datatypes/tests/test_exports.py
@@ -0,0 +1,101 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass (http://github.com/madduck/reclass)
+#
+
+from reclass.settings import Settings
+from reclass.datatypes import Exports, Parameters
+from reclass.errors import ParseError
+import unittest
+
+SETTINGS = Settings()
+
+class TestInvQuery(unittest.TestCase):
+
+    def test_overwrite_method(self):
+        e = Exports({'alpha': { 'one': 1, 'two': 2}}, SETTINGS, '')
+        d = {'alpha': { 'three': 3, 'four': 4}}
+        e.overwrite(d)
+        e.initialise_interpolation()
+        self.assertEqual(e.as_dict(), d)
+
+    def test_malformed_invquery(self):
+        with self.assertRaises(ParseError):
+            p = Parameters({'exp': '$[ exports:a exports:b == self:test_value ]'}, SETTINGS, '')
+        with self.assertRaises(ParseError):
+            p = Parameters({'exp': '$[ exports:a if exports:b self:test_value ]'}, SETTINGS, '')
+        with self.assertRaises(ParseError):
+            p = Parameters({'exp': '$[ exports:a if exports:b == ]'}, SETTINGS, '')
+        with self.assertRaises(ParseError):
+            p = Parameters({'exp': '$[ exports:a if exports:b == self:test_value and exports:c = self:test_value2 ]'}, SETTINGS, '')
+        with self.assertRaises(ParseError):
+            p = Parameters({'exp': '$[ exports:a if exports:b == self:test_value or exports:c == ]'}, SETTINGS, '')
+        with self.assertRaises(ParseError):
+            p = Parameters({'exp': '$[ exports:a if exports:b == self:test_value anddd exports:c == self:test_value2 ]'}, SETTINGS, '')
+
+    def test_value_expr_invquery(self):
+        e = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 4}}
+        p = Parameters({'exp': '$[ exports:a ]'}, SETTINGS, '')
+        r = {'exp': {'node1': 1, 'node2': 3}}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+    def test_if_expr_invquery(self):
+        e = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 4}}
+        p = Parameters({'exp': '$[ exports:a if exports:b == 4 ]'}, SETTINGS, '')
+        r = {'exp': {'node2': 3}}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+    def test_if_expr_invquery_with_refs(self):
+        e = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 4}}
+        p = Parameters({'exp': '$[ exports:a if exports:b == self:test_value ]', 'test_value': 2}, SETTINGS, '')
+        r = {'exp': {'node1': 1}, 'test_value': 2}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+    def test_list_if_expr_invquery(self):
+        e = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 3}, 'node3': {'a': 3, 'b': 2}}
+        p = Parameters({'exp': '$[ if exports:b == 2 ]'}, SETTINGS, '')
+        r = {'exp': ['node1', 'node3']}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+    def test_if_expr_invquery_wth_and(self):
+        e = {'node1': {'a': 1, 'b': 4, 'c': False}, 'node2': {'a': 3, 'b': 4, 'c': True}}
+        p = Parameters({'exp': '$[ exports:a if exports:b == 4 and exports:c == True ]'}, SETTINGS, '')
+        r = {'exp': {'node2': 3}}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+    def test_if_expr_invquery_wth_or(self):
+        e = {'node1': {'a': 1, 'b': 4}, 'node2': {'a': 3, 'b': 3}}
+        p = Parameters({'exp': '$[ exports:a if exports:b == 4 or exports:b == 3 ]'}, SETTINGS, '')
+        r = {'exp': {'node1': 1, 'node2': 3}}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+    def test_list_if_expr_invquery_with_and(self):
+        e = {'node1': {'a': 1, 'b': 2, 'c': 'green'}, 'node2': {'a': 3, 'b': 3}, 'node3': {'a': 3, 'b': 2, 'c': 'red'}}
+        p = Parameters({'exp': '$[ if exports:b == 2 and exports:c == green ]'}, SETTINGS, '')
+        r = {'exp': ['node1']}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+    def test_list_if_expr_invquery_with_and_missing(self):
+        e = {'node1': {'a': 1, 'b': 2, 'c': 'green'}, 'node2': {'a': 3, 'b': 3}, 'node3': {'a': 3, 'b': 2}}
+        p = Parameters({'exp': '$[ if exports:b == 2 and exports:c == green ]'}, SETTINGS, '')
+        r = {'exp': ['node1']}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+    def test_list_if_expr_invquery_with_and(self):
+        e = {'node1': {'a': 1, 'b': 2}, 'node2': {'a': 3, 'b': 3}, 'node3': {'a': 3, 'b': 4}}
+        p = Parameters({'exp': '$[ if exports:b == 2 or exports:b == 4 ]'}, SETTINGS, '')
+        r = {'exp': ['node1', 'node3']}
+        p.interpolate(e)
+        self.assertEqual(p.as_dict(), r)
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/reclass/datatypes/tests/test_parameters.py b/reclass/datatypes/tests/test_parameters.py
index f58056d..9b788dc 100644
--- a/reclass/datatypes/tests/test_parameters.py
+++ b/reclass/datatypes/tests/test_parameters.py
@@ -6,9 +6,14 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+
+import copy
+
+from six import iteritems
+
+from reclass.settings import Settings
 from reclass.datatypes import Parameters
-from reclass.defaults import PARAMETER_INTERPOLATION_SENTINELS
-from reclass.errors import InfiniteRecursionError
+from reclass.errors import InfiniteRecursionError, InterpolationError, ResolveError, ResolveErrorList
 import unittest
 try:
     import unittest.mock as mock
@@ -16,15 +21,29 @@
     import mock
 
 SIMPLE = {'one': 1, 'two': 2, 'three': 3}
+SETTINGS = Settings()
+
+class MockDevice(object):
+    def __init__(self):
+        self._text = ''
+
+    def write(self, s):
+        self._text += s
+        return
+
+    def text(self):
+        return self._text
 
 class TestParameters(unittest.TestCase):
 
-    def _construct_mocked_params(self, iterable=None, delimiter=None):
-        p = Parameters(iterable, delimiter)
+    def _construct_mocked_params(self, iterable=None, settings=SETTINGS):
+        p = Parameters(iterable, settings, '')
         self._base = base = p._base
         p._base = mock.MagicMock(spec_set=dict, wraps=base)
         p._base.__repr__ = mock.MagicMock(autospec=dict.__repr__,
                                           return_value=repr(base))
+        p._base.__getitem__.side_effect = base.__getitem__
+        p._base.__setitem__.side_effect = base.__setitem__
         return p, p._base
 
     def test_len_empty(self):
@@ -44,22 +63,13 @@
     def test_repr_empty(self):
         p, b = self._construct_mocked_params()
         b.__repr__.return_value = repr({})
-        self.assertEqual('%r' % p, '%s(%r, %r)' % (p.__class__.__name__, {},
-                                                   Parameters.DEFAULT_PATH_DELIMITER))
+        self.assertEqual('%r' % p, '%s(%r)' % (p.__class__.__name__, {}))
         b.__repr__.assert_called_once_with()
 
     def test_repr(self):
         p, b = self._construct_mocked_params(SIMPLE)
         b.__repr__.return_value = repr(SIMPLE)
-        self.assertEqual('%r' % p, '%s(%r, %r)' % (p.__class__.__name__, SIMPLE,
-                                                   Parameters.DEFAULT_PATH_DELIMITER))
-        b.__repr__.assert_called_once_with()
-
-    def test_repr_delimiter(self):
-        delim = '%'
-        p, b = self._construct_mocked_params(SIMPLE, delim)
-        b.__repr__.return_value = repr(SIMPLE)
-        self.assertEqual('%r' % p, '%s(%r, %r)' % (p.__class__.__name__, SIMPLE, delim))
+        self.assertEqual('%r' % p, '%s(%r)' % (p.__class__.__name__, SIMPLE))
         b.__repr__.assert_called_once_with()
 
     def test_equal_empty(self):
@@ -71,8 +81,7 @@
 
     def test_equal_default_delimiter(self):
         p1, b1 = self._construct_mocked_params(SIMPLE)
-        p2, b2 = self._construct_mocked_params(SIMPLE,
-                                        Parameters.DEFAULT_PATH_DELIMITER)
+        p2, b2 = self._construct_mocked_params(SIMPLE, SETTINGS)
         b1.__eq__.return_value = True
         self.assertEqual(p1, p2)
         b1.__eq__.assert_called_once_with(b2)
@@ -92,8 +101,10 @@
         b1.__eq__.assert_called_once_with(b2)
 
     def test_unequal_delimiter(self):
-        p1, b1 = self._construct_mocked_params(delimiter=':')
-        p2, b2 = self._construct_mocked_params(delimiter='%')
+        settings1 = Settings({'delimiter': ':'})
+        settings2 = Settings({'delimiter': '%'})
+        p1, b1 = self._construct_mocked_params(settings=settings1)
+        p2, b2 = self._construct_mocked_params(settings=settings2)
         b1.__eq__.return_value = False
         self.assertNotEqual(p1, p2)
         b1.__eq__.assert_called_once_with(b2)
@@ -114,6 +125,7 @@
 
     def test_get_dict(self):
         p, b = self._construct_mocked_params(SIMPLE)
+        p.initialise_interpolation()
         self.assertDictEqual(p.as_dict(), SIMPLE)
 
     def test_merge_scalars(self):
@@ -121,33 +133,37 @@
         mergee = {'five':5,'four':4,'None':None,'tuple':(1,2,3)}
         p2, b2 = self._construct_mocked_params(mergee)
         p1.merge(p2)
-        for key, value in mergee.iteritems():
+        p1.initialise_interpolation()
+        for (key, value) in iteritems(mergee):
             # check that each key, value in mergee resulted in a get call and
             # a __setitem__ call against b1 (the merge target)
             self.assertIn(mock.call(key), b1.get.call_args_list)
             self.assertIn(mock.call(key, value), b1.__setitem__.call_args_list)
 
     def test_stray_occurrence_overwrites_during_interpolation(self):
-        p1 = Parameters({'r' : mock.sentinel.ref, 'b': '${r}'})
-        p2 = Parameters({'b' : mock.sentinel.goal})
+        p1 = Parameters({'r' : mock.sentinel.ref, 'b': '${r}'}, SETTINGS, '')
+        p2 = Parameters({'b' : mock.sentinel.goal}, SETTINGS, '')
         p1.merge(p2)
         p1.interpolate()
         self.assertEqual(p1.as_dict()['b'], mock.sentinel.goal)
 
+
 class TestParametersNoMock(unittest.TestCase):
 
     def test_merge_scalars(self):
-        p = Parameters(SIMPLE)
+        p = Parameters(SIMPLE, SETTINGS, '')
         mergee = {'five':5,'four':4,'None':None,'tuple':(1,2,3)}
         p.merge(mergee)
+        p.initialise_interpolation()
         goal = SIMPLE.copy()
         goal.update(mergee)
         self.assertDictEqual(p.as_dict(), goal)
 
     def test_merge_scalars_overwrite(self):
-        p = Parameters(SIMPLE)
+        p = Parameters(SIMPLE, SETTINGS, '')
         mergee = {'two':5,'four':4,'three':None,'one':(1,2,3)}
         p.merge(mergee)
+        p.initialise_interpolation()
         goal = SIMPLE.copy()
         goal.update(mergee)
         self.assertDictEqual(p.as_dict(), goal)
@@ -155,91 +171,510 @@
     def test_merge_lists(self):
         l1 = [1,2,3]
         l2 = [2,3,4]
-        p1 = Parameters(dict(list=l1[:]))
-        p2 = Parameters(dict(list=l2))
+        p1 = Parameters(dict(list=l1[:]), SETTINGS, '')
+        p2 = Parameters(dict(list=l2), SETTINGS, '')
         p1.merge(p2)
+        p1.initialise_interpolation()
         self.assertListEqual(p1.as_dict()['list'], l1+l2)
 
     def test_merge_list_into_scalar(self):
+        settings = Settings({'allow_list_over_scalar': True})
         l = ['foo', 1, 2]
-        p1 = Parameters(dict(key=l[0]))
-        p1.merge(Parameters(dict(key=l[1:])))
+        p1 = Parameters(dict(key=l[0]), settings, '')
+        p2 = Parameters(dict(key=l[1:]), settings, '')
+        p1.merge(p2)
+        p1.initialise_interpolation()
         self.assertListEqual(p1.as_dict()['key'], l)
 
     def test_merge_scalar_over_list(self):
         l = ['foo', 1, 2]
-        p1 = Parameters(dict(key=l[:2]))
-        p1.merge(Parameters(dict(key=l[2])))
+        settings = Settings({'allow_scalar_over_list': True})
+        p1 = Parameters(dict(key=l[:2]), settings, '')
+        p2 = Parameters(dict(key=l[2]), settings, '')
+        p1.merge(p2)
+        p1.initialise_interpolation()
         self.assertEqual(p1.as_dict()['key'], l[2])
 
+    def test_merge_none_over_list(self):
+        l = ['foo', 1, 2]
+        settings = Settings({'allow_none_override': True})
+        p1 = Parameters(dict(key=l[:2]), settings, '')
+        p2 = Parameters(dict(key=None), settings, '')
+        p1.merge(p2)
+        p1.initialise_interpolation()
+        self.assertEqual(p1.as_dict()['key'], None)
+
+    def test_merge_none_over_list_negative(self):
+        l = ['foo', 1, 2]
+        settings = Settings({'allow_none_override': False})
+        p1 = Parameters(dict(key=l[:2]), settings, '')
+        p2 = Parameters(dict(key=None), settings, '')
+        with self.assertRaises(TypeError):
+            p1.merge(p2)
+            p1.initialise_interpolation()
+
+    def test_merge_none_over_dict(self):
+        settings = Settings({'allow_none_override': True})
+        p1 = Parameters(dict(key=SIMPLE), settings, '')
+        p2 = Parameters(dict(key=None), settings, '')
+        p1.merge(p2)
+        p1.initialise_interpolation()
+        self.assertEqual(p1.as_dict()['key'], None)
+
+    def test_merge_none_over_dict_negative(self):
+        settings = Settings({'allow_none_override': False})
+        p1 = Parameters(dict(key=SIMPLE), settings, '')
+        p2 = Parameters(dict(key=None), settings, '')
+        with self.assertRaises(TypeError):
+            p1.merge(p2)
+            p1.initialise_interpolation()
+
+    # def test_merge_bare_dict_over_dict(self):
+        # settings = Settings({'allow_bare_override': True})
+        # p1 = Parameters(dict(key=SIMPLE), settings, '')
+        # p2 = Parameters(dict(key=dict()), settings, '')
+        # p1.merge(p2)
+        # p1.initialise_interpolation()
+        # self.assertEqual(p1.as_dict()['key'], {})
+
+    # def test_merge_bare_list_over_list(self):
+        # l = ['foo', 1, 2]
+        # settings = Settings({'allow_bare_override': True})
+        # p1 = Parameters(dict(key=l), settings, '')
+        # p2 = Parameters(dict(key=list()), settings, '')
+        # p1.merge(p2)
+        # p1.initialise_interpolation()
+        # self.assertEqual(p1.as_dict()['key'], [])
+
     def test_merge_dicts(self):
         mergee = {'five':5,'four':4,'None':None,'tuple':(1,2,3)}
-        p = Parameters(dict(dict=SIMPLE))
-        p.merge(Parameters(dict(dict=mergee)))
+        p = Parameters(dict(dict=SIMPLE), SETTINGS, '')
+        p2 = Parameters(dict(dict=mergee), SETTINGS, '')
+        p.merge(p2)
+        p.initialise_interpolation()
         goal = SIMPLE.copy()
         goal.update(mergee)
         self.assertDictEqual(p.as_dict(), dict(dict=goal))
 
     def test_merge_dicts_overwrite(self):
         mergee = {'two':5,'four':4,'three':None,'one':(1,2,3)}
-        p = Parameters(dict(dict=SIMPLE))
-        p.merge(Parameters(dict(dict=mergee)))
+        p = Parameters(dict(dict=SIMPLE), SETTINGS, '')
+        p2 = Parameters(dict(dict=mergee), SETTINGS, '')
+        p.merge(p2)
+        p.initialise_interpolation()
         goal = SIMPLE.copy()
         goal.update(mergee)
         self.assertDictEqual(p.as_dict(), dict(dict=goal))
 
+    def test_merge_dicts_override(self):
+        """Validate that tilde merge overrides function properly."""
+        mergee = {'~one': {'a': 'alpha'},
+                  '~two': ['gamma']}
+        base = {'one': {'b': 'beta'},
+                'two': ['delta']}
+        goal = {'one': {'a': 'alpha'},
+                'two': ['gamma']}
+        p = Parameters(dict(dict=base), SETTINGS, '')
+        p2 = Parameters(dict(dict=mergee), SETTINGS, '')
+        p.merge(p2)
+        p.initialise_interpolation()
+        self.assertDictEqual(p.as_dict(), dict(dict=goal))
+
     def test_merge_dict_into_scalar(self):
-        p = Parameters(dict(base='foo'))
+        p = Parameters(dict(base='foo'), SETTINGS, '')
+        p2 = Parameters(dict(base=SIMPLE), SETTINGS, '')
         with self.assertRaises(TypeError):
-            p.merge(Parameters(dict(base=SIMPLE)))
+            p.merge(p2)
+            p.interpolate()
 
     def test_merge_scalar_over_dict(self):
-        p = Parameters(dict(base=SIMPLE))
+        settings = Settings({'allow_scalar_over_dict': True})
+        p = Parameters(dict(base=SIMPLE), settings, '')
         mergee = {'base':'foo'}
-        p.merge(Parameters(mergee))
+        p2 = Parameters(mergee, settings, '')
+        p.merge(p2)
+        p.initialise_interpolation()
         self.assertDictEqual(p.as_dict(), mergee)
 
     def test_interpolate_single(self):
         v = 42
-        d = {'foo': 'bar'.join(PARAMETER_INTERPOLATION_SENTINELS),
+        d = {'foo': 'bar'.join(SETTINGS.reference_sentinels),
              'bar': v}
-        p = Parameters(d)
+        p = Parameters(d, SETTINGS, '')
         p.interpolate()
         self.assertEqual(p.as_dict()['foo'], v)
 
     def test_interpolate_multiple(self):
         v = '42'
-        d = {'foo': 'bar'.join(PARAMETER_INTERPOLATION_SENTINELS) + 'meep'.join(PARAMETER_INTERPOLATION_SENTINELS),
+        d = {'foo': 'bar'.join(SETTINGS.reference_sentinels) + 'meep'.join(SETTINGS.reference_sentinels),
              'bar': v[0],
              'meep': v[1]}
-        p = Parameters(d)
+        p = Parameters(d, SETTINGS, '')
         p.interpolate()
         self.assertEqual(p.as_dict()['foo'], v)
 
     def test_interpolate_multilevel(self):
         v = 42
-        d = {'foo': 'bar'.join(PARAMETER_INTERPOLATION_SENTINELS),
-             'bar': 'meep'.join(PARAMETER_INTERPOLATION_SENTINELS),
+        d = {'foo': 'bar'.join(SETTINGS.reference_sentinels),
+             'bar': 'meep'.join(SETTINGS.reference_sentinels),
              'meep': v}
-        p = Parameters(d)
+        p = Parameters(d, SETTINGS, '')
         p.interpolate()
         self.assertEqual(p.as_dict()['foo'], v)
 
     def test_interpolate_list(self):
-        l = [41,42,43]
-        d = {'foo': 'bar'.join(PARAMETER_INTERPOLATION_SENTINELS),
+        l = [41, 42, 43]
+        d = {'foo': 'bar'.join(SETTINGS.reference_sentinels),
              'bar': l}
-        p = Parameters(d)
+        p = Parameters(d, SETTINGS, '')
         p.interpolate()
         self.assertEqual(p.as_dict()['foo'], l)
 
     def test_interpolate_infrecursion(self):
         v = 42
-        d = {'foo': 'bar'.join(PARAMETER_INTERPOLATION_SENTINELS),
-             'bar': 'foo'.join(PARAMETER_INTERPOLATION_SENTINELS)}
-        p = Parameters(d)
+        d = {'foo': 'bar'.join(SETTINGS.reference_sentinels),
+             'bar': 'foo'.join(SETTINGS.reference_sentinels)}
+        p = Parameters(d, SETTINGS, '')
         with self.assertRaises(InfiniteRecursionError):
             p.interpolate()
 
+    def test_nested_references(self):
+        d = {'a': '${${z}}', 'b': 2, 'z': 'b'}
+        r = {'a': 2, 'b': 2, 'z': 'b'}
+        p = Parameters(d, SETTINGS, '')
+        p.interpolate()
+        self.assertEqual(p.as_dict(), r)
+
+    def test_nested_deep_references(self):
+        d = {'one': { 'a': 1, 'b': '${one:${one:c}}', 'c': 'a' } }
+        r = {'one': { 'a': 1, 'b': 1, 'c': 'a'} }
+        p = Parameters(d, SETTINGS, '')
+        p.interpolate()
+        self.assertEqual(p.as_dict(), r)
+
+    def test_stray_occurrence_overwrites_during_interpolation(self):
+        p1 = Parameters({'r' : 1, 'b': '${r}'}, SETTINGS, '')
+        p2 = Parameters({'b' : 2}, SETTINGS, '')
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict()['b'], 2)
+
+    def test_referenced_dict_deep_overwrite(self):
+        p1 = Parameters({'alpha': {'one': {'a': 1, 'b': 2} } }, SETTINGS, '')
+        p2 = Parameters({'beta': '${alpha}'}, SETTINGS, '')
+        p3 = Parameters({'alpha': {'one': {'c': 3, 'd': 4} },
+                         'beta':  {'one': {'a': 99} } }, SETTINGS, '')
+        r = {'alpha': {'one': {'a':1, 'b': 2, 'c': 3, 'd':4} },
+             'beta': {'one': {'a':99, 'b': 2, 'c': 3, 'd':4} } }
+        p1.merge(p2)
+        p1.merge(p3)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_complex_reference_overwriting(self):
+        p1 = Parameters({'one': 'abc_123_${two}_${three}', 'two': 'XYZ', 'four': 4}, SETTINGS, '')
+        p2 = Parameters({'one': 'QWERTY_${three}_${four}', 'three': '999'}, SETTINGS, '')
+        r = {'one': 'QWERTY_999_4', 'two': 'XYZ', 'three': '999', 'four': 4}
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_nested_reference_with_overwriting(self):
+        p1 = Parameters({'one': {'a': 1, 'b': 2, 'z': 'a'},
+                         'two': '${one:${one:z}}' }, SETTINGS, '')
+        p2 = Parameters({'one': {'z': 'b'} }, SETTINGS, '')
+        r = {'one': {'a': 1, 'b':2, 'z': 'b'}, 'two': 2}
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_merge_referenced_lists(self):
+        p1 = Parameters({'one': [ 1, 2, 3 ], 'two': [ 4, 5, 6 ], 'three': '${one}'}, SETTINGS, '')
+        p2 = Parameters({'three': '${two}'}, SETTINGS, '')
+        r = {'one': [ 1, 2, 3 ], 'two': [ 4, 5, 6], 'three': [ 1, 2, 3, 4, 5, 6 ]}
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_merge_referenced_dicts(self):
+        p1 = Parameters({'one': {'a': 1, 'b': 2}, 'two': {'c': 3, 'd': 4}, 'three': '${one}'}, SETTINGS, '')
+        p2 = Parameters({'three': '${two}'}, SETTINGS, '')
+        r = {'one': {'a': 1, 'b': 2}, 'two': {'c': 3, 'd': 4}, 'three': {'a': 1, 'b': 2, 'c': 3, 'd': 4}}
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_deep_refs_in_referenced_dicts(self):
+        p = Parameters({'A': '${C:a}', 'B': {'a': 1, 'b': 2}, 'C': '${B}'}, SETTINGS, '')
+        r = {'A': 1, 'B': {'a': 1, 'b': 2}, 'C': {'a': 1, 'b': 2}}
+        p.interpolate()
+        self.assertEqual(p.as_dict(), r)
+
+    def test_overwrite_none(self):
+        p1 = Parameters({'A': None, 'B': None, 'C': None, 'D': None, 'E': None, 'F': None}, SETTINGS, '')
+        p2 = Parameters({'A': 'abc', 'B': [1, 2, 3], 'C': {'a': 'aaa', 'b': 'bbb'}, 'D': '${A}', 'E': '${B}', 'F': '${C}'}, SETTINGS, '')
+        r = {'A': 'abc', 'B': [1, 2, 3], 'C': {'a': 'aaa', 'b': 'bbb'}, 'D': 'abc', 'E': [1, 2, 3], 'F': {'a': 'aaa', 'b': 'bbb'}}
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_interpolate_escaping(self):
+        v = 'bar'.join(SETTINGS.reference_sentinels)
+        d = {'foo': SETTINGS.escape_character + 'bar'.join(SETTINGS.reference_sentinels),
+             'bar': 'unused'}
+        p = Parameters(d, SETTINGS, '')
+        p.initialise_interpolation()
+        self.assertEqual(p.as_dict()['foo'], v)
+
+    def test_interpolate_double_escaping(self):
+        v = SETTINGS.escape_character + 'meep'
+        d = {'foo': SETTINGS.escape_character + SETTINGS.escape_character + 'bar'.join(SETTINGS.reference_sentinels),
+             'bar': 'meep'}
+        p = Parameters(d, SETTINGS, '')
+        p.interpolate()
+        self.assertEqual(p.as_dict()['foo'], v)
+
+    def test_interpolate_escaping_backwards_compatibility(self):
+        """In all following cases, escaping should not happen and the escape character
+        needs to be printed as-is, to ensure backwards compatibility to older versions."""
+        v = ' '.join([
+            # Escape character followed by unescapable character
+            '1', SETTINGS.escape_character,
+            # Escape character followed by escape character
+            '2', SETTINGS.escape_character + SETTINGS.escape_character,
+            # Escape character followed by interpolation end sentinel
+            '3', SETTINGS.escape_character + SETTINGS.reference_sentinels[1],
+            # Escape character at the end of the string
+            '4', SETTINGS.escape_character
+            ])
+        d = {'foo': v}
+        p = Parameters(d, SETTINGS, '')
+        p.initialise_interpolation()
+        self.assertEqual(p.as_dict()['foo'], v)
+
+    def test_escape_close_in_ref(self):
+        p1 = Parameters({'one}': 1, 'two': '${one\\}}'}, SETTINGS, '')
+        r = {'one}': 1, 'two': 1}
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_double_escape_in_ref(self):
+        d = {'one\\': 1, 'two': '${one\\\\}'}
+        p1 = Parameters(d, SETTINGS, '')
+        r = {'one\\': 1, 'two': 1}
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_merging_for_multiple_nodes(self):
+        p1 = Parameters({ 'alpha': { 'one': 111 }}, SETTINGS, '')
+        p2 = Parameters({ 'beta': {'two': '${alpha:one}' }}, SETTINGS, '')
+        p3 = Parameters({ 'beta': {'two': 222 }}, SETTINGS, '')
+        n1 = Parameters({ 'name': 'node1'}, SETTINGS, '')
+        r1 = { 'alpha': { 'one': 111 }, 'beta': { 'two': 111 }, 'name': 'node1' }
+        r2 = { 'alpha': { 'one': 111 }, 'beta': { 'two': 222 }, 'name': 'node2' }
+        n1.merge(p1)
+        n1.merge(p2)
+        n1.interpolate()
+        n2 = Parameters({'name': 'node2'}, SETTINGS, '')
+        n2.merge(p1)
+        n2.merge(p2)
+        n2.merge(p3)
+        n2.interpolate()
+        self.assertEqual(n1.as_dict(), r1)
+        self.assertEqual(n2.as_dict(), r2)
+
+    def test_list_merging_for_multiple_nodes(self):
+        p1 = Parameters({ 'alpha': { 'one': [1, 2] }}, SETTINGS, '')
+        p2 = Parameters({ 'beta': {'two': '${alpha:one}' }}, SETTINGS, '')
+        p3 = Parameters({ 'beta': {'two': [3] }}, SETTINGS, '')
+        n1 = Parameters({ 'name': 'node1'}, SETTINGS, '')
+        r1 = { 'alpha': { 'one': [1, 2] }, 'beta': { 'two': [1, 2] }, 'name': 'node1' }
+        r2 = { 'alpha': { 'one': [1, 2] }, 'beta': { 'two': [1, 2, 3] }, 'name': 'node2' }
+        n1.merge(p1)
+        n1.merge(p2)
+        n1.interpolate()
+        n2 = Parameters({'name': 'node2'}, SETTINGS, '')
+        n2.merge(p1)
+        n2.merge(p2)
+        n2.merge(p3)
+        n2.interpolate()
+        self.assertEqual(n1.as_dict(), r1)
+        self.assertEqual(n2.as_dict(), r2)
+
+    def test_dict_merging_for_multiple_nodes(self):
+        p1 = Parameters({ 'alpha': { 'one': { 'a': 'aa', 'b': 'bb' }}}, SETTINGS, '')
+        p2 = Parameters({ 'beta': {'two': '${alpha:one}' }}, SETTINGS, '')
+        p3 = Parameters({ 'beta': {'two': {'c': 'cc' }}}, SETTINGS, '')
+        n1 = Parameters({ 'name': 'node1'}, SETTINGS, '')
+        r1 = { 'alpha': { 'one': {'a': 'aa', 'b': 'bb'} }, 'beta': { 'two': {'a': 'aa', 'b': 'bb'} }, 'name': 'node1' }
+        r2 = { 'alpha': { 'one': {'a': 'aa', 'b': 'bb'} }, 'beta': { 'two': {'a': 'aa', 'b': 'bb', 'c': 'cc'} }, 'name': 'node2' }
+        n1.merge(p1)
+        n1.merge(p2)
+        n1.interpolate()
+        n2 = Parameters({'name': 'node2'}, SETTINGS, '')
+        n2.merge(p1)
+        n2.merge(p2)
+        n2.merge(p3)
+        n2.interpolate()
+        self.assertEqual(n1.as_dict(), r1)
+        self.assertEqual(n2.as_dict(), r2)
+
+    def test_list_merging_with_refs_for_multiple_nodes(self):
+        p1 = Parameters({ 'alpha': { 'one': [1, 2], 'two': [3, 4] }}, SETTINGS, '')
+        p2 = Parameters({ 'beta': { 'three': '${alpha:one}' }}, SETTINGS, '')
+        p3 = Parameters({ 'beta': { 'three': '${alpha:two}' }}, SETTINGS, '')
+        p4 = Parameters({ 'beta': { 'three': '${alpha:one}' }}, SETTINGS, '')
+        n1 = Parameters({ 'name': 'node1' }, SETTINGS, '')
+        r1 = {'alpha': {'one': [1, 2], 'two': [3, 4]}, 'beta': {'three': [1, 2]}, 'name': 'node1'}
+        r2 = {'alpha': {'one': [1, 2], 'two': [3, 4]}, 'beta': {'three': [1, 2, 3, 4, 1, 2]}, 'name': 'node2'}
+        n2 = Parameters({ 'name': 'node2' }, SETTINGS, '')
+        n2.merge(p1)
+        n2.merge(p2)
+        n2.merge(p3)
+        n2.merge(p4)
+        n2.interpolate()
+        n1.merge(p1)
+        n1.merge(p2)
+        n1.interpolate()
+        self.assertEqual(n1.as_dict(), r1)
+        self.assertEqual(n2.as_dict(), r2)
+
+    def test_nested_refs_with_multiple_nodes(self):
+        p1 = Parameters({ 'alpha': { 'one': 1, 'two': 2 } }, SETTINGS, '')
+        p2 = Parameters({ 'beta': { 'three': 'one' } }, SETTINGS, '')
+        p3 = Parameters({ 'beta': { 'three': 'two' } }, SETTINGS, '')
+        p4 = Parameters({ 'beta': { 'four': '${alpha:${beta:three}}' } }, SETTINGS, '')
+        n1 = Parameters({ 'name': 'node1' }, SETTINGS, '')
+        r1 = {'alpha': {'one': 1, 'two': 2}, 'beta': {'three': 'one', 'four': 1}, 'name': 'node1'}
+        r2 = {'alpha': {'one': 1, 'two': 2}, 'beta': {'three': 'two', 'four': 2}, 'name': 'node2'}
+        n1.merge(p1)
+        n1.merge(p4)
+        n1.merge(p2)
+        n1.interpolate()
+        n2 = Parameters({ 'name': 'node2' }, SETTINGS, '')
+        n2.merge(p1)
+        n2.merge(p4)
+        n2.merge(p3)
+        n2.interpolate()
+        self.assertEqual(n1.as_dict(), r1)
+        self.assertEqual(n2.as_dict(), r2)
+
+    def test_nested_refs_error_message(self):
+        # beta is missing, oops
+        p1 = Parameters({'alpha': {'one': 1, 'two': 2}, 'gamma': '${alpha:${beta}}'}, SETTINGS, '')
+        with self.assertRaises(InterpolationError) as error:
+            p1.interpolate()
+        self.assertEqual(error.exception.message, "-> \n   Bad references, at gamma\n      ${beta}")
+
+    def test_multiple_resolve_errors(self):
+        p1 = Parameters({'alpha': '${gamma}', 'beta': '${gamma}'}, SETTINGS, '')
+        with self.assertRaises(ResolveErrorList) as error:
+            p1.interpolate()
+        self.assertEqual(error.exception.message, "-> \n   Cannot resolve ${gamma}, at alpha\n   Cannot resolve ${gamma}, at beta")
+
+    def test_force_single_resolve_error(self):
+        settings = copy.deepcopy(SETTINGS)
+        settings.group_errors = False
+        p1 = Parameters({'alpha': '${gamma}', 'beta': '${gamma}'}, settings, '')
+        with self.assertRaises(ResolveError) as error:
+            p1.interpolate()
+        self.assertEqual(error.exception.message, "-> \n   Cannot resolve ${gamma}, at alpha")
+
+    def test_ignore_overwriten_missing_reference(self):
+        settings = copy.deepcopy(SETTINGS)
+        settings.ignore_overwritten_missing_references = True
+        p1 = Parameters({'alpha': '${beta}'}, settings, '')
+        p2 = Parameters({'alpha': '${gamma}'}, settings, '')
+        p3 = Parameters({'gamma': 3}, settings, '')
+        r1 = {'alpha': 3, 'gamma': 3}
+        p1.merge(p2)
+        p1.merge(p3)
+        err1 = "[WARNING] Reference '${beta}' undefined\n"
+        with mock.patch('sys.stderr', new=MockDevice()) as std_err:
+            p1.interpolate()
+        self.assertEqual(p1.as_dict(), r1)
+        self.assertEqual(std_err.text(), err1)
+
+    def test_ignore_overwriten_missing_reference_last_value(self):
+        # an error should be raised if the last reference to be merged
+        # is missing even if ignore_overwritten_missing_references is true
+        settings = copy.deepcopy(SETTINGS)
+        settings.ignore_overwritten_missing_references = True
+        p1 = Parameters({'alpha': '${gamma}'}, settings, '')
+        p2 = Parameters({'alpha': '${beta}'}, settings, '')
+        p3 = Parameters({'gamma': 3}, settings, '')
+        p1.merge(p2)
+        p1.merge(p3)
+        with self.assertRaises(InterpolationError) as error:
+            p1.interpolate()
+        self.assertEqual(error.exception.message, "-> \n   Cannot resolve ${beta}, at alpha")
+
+    def test_ignore_overwriten_missing_reference_dict(self):
+        # setting ignore_overwritten_missing_references to true should
+        # not change the behaviour for dicts
+        settings = copy.deepcopy(SETTINGS)
+        settings.ignore_overwritten_missing_references = True
+        p1 = Parameters({'alpha': '${beta}'}, settings, '')
+        p2 = Parameters({'alpha': '${gamma}'}, settings, '')
+        p3 = Parameters({'gamma': {'one': 1, 'two': 2}}, settings, '')
+        err1 = "[WARNING] Reference '${beta}' undefined\n"
+        p1.merge(p2)
+        p1.merge(p3)
+        with self.assertRaises(InterpolationError) as error, mock.patch('sys.stderr', new=MockDevice()) as std_err:
+            p1.interpolate()
+        self.assertEqual(error.exception.message, "-> \n   Cannot resolve ${beta}, at alpha")
+        self.assertEqual(std_err.text(), err1)
+
+    def test_escaped_string_in_ref_dict_1(self):
+        # test with escaped string in first dict to be merged
+        p1 = Parameters({'a': { 'one': '${a_ref}' }, 'b': { 'two': '\${not_a_ref}' }, 'c': '${b}', 'a_ref': 123}, SETTINGS, '')
+        p2 = Parameters({'c': '${a}'}, SETTINGS, '')
+        r = { 'a': { 'one': 123 }, 'b': { 'two': '${not_a_ref}' }, 'c': { 'one': 123, 'two': '${not_a_ref}' }, 'a_ref': 123}
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_escaped_string_in_ref_dict_2(self):
+        # test with escaped string in second dict to be merged
+        p1 = Parameters({'a': { 'one': '${a_ref}' }, 'b': { 'two': '\${not_a_ref}' }, 'c': '${a}', 'a_ref': 123}, SETTINGS, '')
+        p2 = Parameters({'c': '${b}'}, SETTINGS, '')
+        r = { 'a': { 'one': 123 }, 'b': { 'two': '${not_a_ref}' }, 'c': { 'one': 123, 'two': '${not_a_ref}' }, 'a_ref': 123}
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_complex_overwrites_1(self):
+        # find a better name for this test
+        p1 = Parameters({ 'test': { 'dict': { 'a': '${values:one}', 'b': '${values:two}' } },
+                          'values': { 'one': 1, 'two': 2, 'three': { 'x': 'X', 'y': 'Y' } } }, SETTINGS, '')
+        p2 = Parameters({ 'test': { 'dict': { 'c': '${values:two}' } } }, SETTINGS, '')
+        p3 = Parameters({ 'test': { 'dict': { '~b': '${values:three}' } } }, SETTINGS, '')
+        r = {'test': {'dict': {'a': 1, 'b': {'x': 'X', 'y': 'Y'}, 'c': 2}}, 'values': {'one': 1, 'three': {'x': 'X', 'y': 'Y'}, 'two': 2} }
+        p2.merge(p3)
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_escaped_string_overwrites(self):
+        p1 = Parameters({ 'test': '\${not_a_ref}' }, SETTINGS, '')
+        p2 = Parameters({ 'test': '\${also_not_a_ref}' }, SETTINGS, '')
+        r = { 'test': '${also_not_a_ref}' }
+        p1.merge(p2)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+    def test_escaped_string_in_ref_dict_overwrite(self):
+        p1 = Parameters({'a': { 'one': '\${not_a_ref}' }, 'b': { 'two': '\${also_not_a_ref}' }}, SETTINGS, '')
+        p2 = Parameters({'c': '${a}'}, SETTINGS, '')
+        p3 = Parameters({'c': '${b}'}, SETTINGS, '')
+        p4 = Parameters({'c': { 'one': '\${again_not_a_ref}' } }, SETTINGS, '')
+        r = {'a': {'one': '${not_a_ref}'}, 'b': {'two': '${also_not_a_ref}'}, 'c': {'one': '${again_not_a_ref}', 'two': '${also_not_a_ref}'}}
+        p1.merge(p2)
+        p1.merge(p3)
+        p1.merge(p4)
+        p1.interpolate()
+        self.assertEqual(p1.as_dict(), r)
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/reclass/defaults.py b/reclass/defaults.py
index d066290..408307d 100644
--- a/reclass/defaults.py
+++ b/reclass/defaults.py
@@ -7,7 +7,7 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 import os, sys
-from version import RECLASS_NAME
+from .version import RECLASS_NAME
 
 # defaults for the command-line options
 OPT_STORAGE_TYPE = 'yaml_fs'
@@ -15,8 +15,25 @@
 OPT_NODES_URI = 'nodes'
 OPT_CLASSES_URI = 'classes'
 OPT_PRETTY_PRINT = True
+OPT_GROUP_ERRORS = True
+OPT_NO_REFS = False
 OPT_OUTPUT = 'yaml'
 
+OPT_IGNORE_CLASS_NOTFOUND = False
+OPT_IGNORE_CLASS_NOTFOUND_REGEXP = ['.*']
+OPT_IGNORE_CLASS_NOTFOUND_WARNING = True
+
+OPT_IGNORE_OVERWRITTEN_MISSING_REFERENCES = True
+
+OPT_ALLOW_SCALAR_OVER_DICT = False
+OPT_ALLOW_SCALAR_OVER_LIST = False
+OPT_ALLOW_LIST_OVER_SCALAR = False
+OPT_ALLOW_DICT_OVER_SCALAR = False
+OPT_ALLOW_NONE_OVERRIDE = False
+
+OPT_INVENTORY_IGNORE_FAILED_NODE = False
+OPT_INVENTORY_IGNORE_FAILED_RENDER = False
+
 CONFIG_FILE_SEARCH_PATH = [os.getcwd(),
                            os.path.expanduser('~'),
                            OPT_INVENTORY_BASE_URI,
@@ -24,5 +41,11 @@
                           ]
 CONFIG_FILE_NAME = RECLASS_NAME + '-config.yml'
 
-PARAMETER_INTERPOLATION_SENTINELS = ('${', '}')
+REFERENCE_SENTINELS = ('${', '}')
+EXPORT_SENTINELS = ('$[', ']')
 PARAMETER_INTERPOLATION_DELIMITER = ':'
+PARAMETER_DICT_KEY_OVERRIDE_PREFIX = '~'
+ESCAPE_CHARACTER = '\\'
+
+AUTOMATIC_RECLASS_PARAMETERS = True
+DEFAULT_ENVIRONMENT = 'base'
diff --git a/reclass/errors.py b/reclass/errors.py
index 4da2bc3..349e242 100644
--- a/reclass/errors.py
+++ b/reclass/errors.py
@@ -10,19 +10,26 @@
 import posix, sys
 import traceback
 
-from reclass.defaults import PARAMETER_INTERPOLATION_SENTINELS
+from reclass.defaults import REFERENCE_SENTINELS, EXPORT_SENTINELS
 
 class ReclassException(Exception):
 
-    def __init__(self, rc=posix.EX_SOFTWARE, msg=None):
+    def __init__(self, rc=posix.EX_SOFTWARE, msg=None, tbFlag=True):
         super(ReclassException, self).__init__()
         self._rc = rc
         self._msg = msg
-        self._traceback = traceback.format_exc()
+        if tbFlag:
+            self._traceback = traceback.format_exc()
+        else:
+            self._traceback = None
+        self._full_traceback = False
 
     message = property(lambda self: self._get_message())
     rc = property(lambda self: self._rc)
 
+    def __str__(self):
+        return self.message + '\n' + super(ReclassException, self).__str__()
+
     def _get_message(self):
         if self._msg:
             return self._msg
@@ -30,9 +37,16 @@
             return 'No error message provided.'
 
     def exit_with_message(self, out=sys.stderr):
-        print >>out, self.message
+        if self._full_traceback:
+            t, v, tb = sys.exc_info()
+            print >>out, 'Full Traceback:'
+            for l in traceback.format_tb(tb):
+                print >>out, l,
+            print >>out
         if self._traceback:
             print >>out, self._traceback
+        print >>out, self.message
+        print >>out
         sys.exit(self.rc)
 
 
@@ -89,81 +103,190 @@
 
     def __init__(self, storage, nodename, uri):
         super(NodeNotFound, self).__init__(msg=None)
-        self._storage = storage
-        self._name = nodename
-        self._uri = uri
+        self.storage = storage
+        self.name = nodename
+        self.uri = uri
 
     def _get_message(self):
         msg = "Node '{0}' not found under {1}://{2}"
-        return msg.format(self._name, self._storage, self._uri)
-
-
-class ClassNotFound(NotFoundError):
-
-    def __init__(self, storage, classname, uri, nodename=None):
-        super(ClassNotFound, self).__init__(msg=None)
-        self._storage = storage
-        self._name = classname
-        self._uri = uri
-        self._nodename = nodename
-
-    def _get_message(self):
-        if self._nodename:
-            msg = "Class '{0}' (in ancestry of node '{1}') not found " \
-                  "under {2}://{3}"
-        else:
-            msg = "Class '{0}' not found under {2}://{3}"
-        return msg.format(self._name, self._nodename, self._storage, self._uri)
-
-    def set_nodename(self, nodename):
-        self._nodename = nodename
+        return msg.format(self.name, self.storage, self.uri)
 
 
 class InterpolationError(ReclassException):
 
-    def __init__(self, msg, rc=posix.EX_DATAERR):
-        super(InterpolationError, self).__init__(rc=rc, msg=msg)
-
-
-class UndefinedVariableError(InterpolationError):
-
-    def __init__(self, var, context=None):
-        super(UndefinedVariableError, self).__init__(msg=None)
-        self._var = var
-        self._context = context
+    def __init__(self, msg, rc=posix.EX_DATAERR, nodename='', uri=None, context=None, tbFlag=True):
+        super(InterpolationError, self).__init__(rc=rc, msg=msg, tbFlag=tbFlag)
+        self.nodename = nodename
+        self.uri = uri
+        self.context = context
 
     def _get_message(self):
-        msg = "Cannot resolve " + var.join(PARAMETER_INTERPOLATION_SENTINELS)
-        if self._context:
-            msg += ' in the context of %s' % self._context
+        msg = '-> {0}\n'.format(self.nodename)
+        msg += self._render_error_message(self._get_error_message(), 1)
+        msg = msg[:-1]
         return msg
 
-    def set_context(self, context):
-        self._context = context
+    def _render_error_message(self, message_list, indent):
+        msg = ''
+        for l in message_list:
+            if isinstance(l, list):
+                msg += self._render_error_message(l, indent + 1)
+            else:
+                msg += (' ' * indent * 3) + l + '\n'
+        return msg
+
+    def _add_context_and_uri(self):
+        msg = ''
+        if self.context:
+            msg += ', at %s' % self.context
+        if self.uri:
+            msg += ', in %s' % self.uri
+        return msg
 
 
-class IncompleteInterpolationError(InterpolationError):
+class ClassNotFound(InterpolationError):
 
-    def __init__(self, string, end_sentinel):
-        super(IncompleteInterpolationError, self).__init__(msg=None)
-        self._ref = string.join(PARAMETER_INTERPOLATION_SENTINELS)
-        self._end_sentinel = end_sentinel
+    def __init__(self, storage, classname, path, nodename='', uri=None):
+        super(ClassNotFound, self).__init__(msg=None, uri=uri, nodename=nodename)
+        self.storage = storage
+        self.name = classname
+        self.path = path
 
-    def _get_message(self):
-        msg = "Missing '{0}' to end reference: {1}"
-        return msg.format(self._end_sentinel, self._ref)
+    def _get_error_message(self):
+        msg = [ 'In {0}'.format(self.uri),
+                'Class {0} not found under {1}://{2}'.format(self.name, self.storage, self.path) ]
+        return msg
+
+
+class ClassNameResolveError(InterpolationError):
+    def __init__(self, classname, nodename, uri):
+        super(ClassNameResolveError, self).__init__(msg=None, uri=uri, nodename=nodename)
+        self.name = classname
+
+    def _get_error_message(self):
+        msg = [ 'In {0}'.format(self.uri),
+                'Class name {0} not resolvable'.format(self.name) ]
+        return msg
+
+
+class InvQueryClassNotFound(InterpolationError):
+
+    def __init__(self, classNotFoundError, nodename=''):
+        super(InvQueryClassNotFound, self).__init__(msg=None, nodename=nodename)
+        self.classNotFoundError = classNotFoundError
+        self._traceback = self.classNotFoundError._traceback
+
+    def _get_error_message(self):
+        msg = [ 'Inventory Queries:',
+                '-> {0}'.format(self.classNotFoundError.nodename) ]
+        msg.append(self.classNotFoundError._get_error_message())
+        return msg
+
+
+class InvQueryClassNameResolveError(InterpolationError):
+    def __init__(self, classNameResolveError, nodename=''):
+        super(InvQueryClassNameResolveError, self).__init__(msg=None, nodename=nodename)
+        self.classNameResolveError = classNameResolveError
+        self._traceback = self.classNameResolveError._traceback
+
+    def _get_error_message(self):
+        msg = [ 'Inventory Queries:',
+                '-> {0}'.format(self.classNameResolveError.nodename) ]
+        msg.append(self.classNameResolveError._get_error_message())
+        return msg
+
+
+class ResolveError(InterpolationError):
+
+    def __init__(self, reference, uri=None, context=None):
+        super(ResolveError, self).__init__(msg=None)
+        self.reference = reference
+
+    def _get_error_message(self):
+        msg = 'Cannot resolve {0}'.format(self.reference.join(REFERENCE_SENTINELS)) + self._add_context_and_uri()
+        return [ msg ]
+
+class ResolveErrorList(InterpolationError):
+    def __init__(self):
+        super(ResolveErrorList, self).__init__(msg=None)
+        self.resolve_errors = []
+        self._traceback = False
+
+    def add(self, resolve_error):
+        self.resolve_errors.append(resolve_error)
+
+    def have_errors(self):
+        return len(self.resolve_errors) > 0
+
+    def _get_error_message(self):
+        msgs = []
+        for e in self.resolve_errors:
+            msgs.extend(e._get_error_message())
+        return msgs
+
+
+class InvQueryError(InterpolationError):
+
+    def __init__(self, query, resolveError, uri=None, context=None):
+        super(InvQueryError, self).__init__(msg=None)
+        self.query = query
+        self.resolveError = resolveError
+        self._traceback = self.resolveError._traceback
+
+    def _get_error_message(self):
+        msg1 = 'Failed inv query {0}'.format(self.query.join(EXPORT_SENTINELS)) + self._add_context_and_uri()
+        msg2 = '-> {0}'.format(self.resolveError.nodename)
+        msg3 = self.resolveError._get_error_message()
+        return [ msg1, msg2, msg3 ]
+
+
+class ParseError(InterpolationError):
+
+    def __init__(self, msg, line, col, lineno, rc=posix.EX_DATAERR):
+        super(ParseError, self).__init__(rc=rc, msg=None)
+        self._err = msg
+        self._line = line
+        self._col = col
+        self._lineno = lineno
+
+    def _get_error_message(self):
+        msg = [ 'Parse error: {0}'.format(self._line.join(EXPORT_SENTINELS)) + self._add_context_and_uri() ]
+        msg.append('{0} at char {1}'.format(self._err, self._col - 1))
 
 
 class InfiniteRecursionError(InterpolationError):
 
-    def __init__(self, path, ref):
-        super(InfiniteRecursionError, self).__init__(msg=None)
-        self._path = path
-        self._ref = ref.join(PARAMETER_INTERPOLATION_SENTINELS)
+    def __init__(self, context, ref, uri):
+        super(InfiniteRecursionError, self).__init__(msg=None, tbFlag=False, uri=uri)
+        self.context = context
+        self.ref = ref
 
-    def _get_message(self):
-        msg = "Infinite recursion while resolving {0} at {1}"
-        return msg.format(self._ref, self._path)
+    def _get_error_message(self):
+        msg = [ 'Infinite recursion: {0}'.format(self.ref.join(REFERENCE_SENTINELS)) + self._add_context_and_uri() ]
+        return msg
+
+
+class BadReferencesError(InterpolationError):
+
+    def __init__(self, refs, context, uri):
+        super(BadReferencesError, self).__init__(msg=None, context=context, uri=uri, tbFlag=False)
+        self.refs = [ r.join(REFERENCE_SENTINELS) for r in refs ]
+
+    def _get_error_message(self):
+        msg = [ 'Bad references' + self._add_context_and_uri(),
+                '   ' + ', '.join(self.refs) ]
+        return msg
+
+
+class ExpressionError(InterpolationError):
+
+    def __init__(self, msg, rc=posix.EX_DATAERR, tbFlag=True):
+        super(ExpressionError, self).__init__(rc=rc, msg=None, tbFlag=tbFlag)
+        self._error_msg = msg
+
+    def _get_error_message(self):
+        msg = [ 'Expression error: {0}'.format(self._error_msg) + self._add_context_and_uri() ]
+        return msg
 
 
 class MappingError(ReclassException):
@@ -193,7 +316,7 @@
 
     def _get_message(self):
         msg = "Invalid character '{0}' in class name '{1}'."
-        return msg.format(self._char, classname)
+        return msg.format(self._char, self._classname)
 
 
 class DuplicateNodeNameError(NameError):
diff --git a/reclass/output/__init__.py b/reclass/output/__init__.py
index 58cd101..42fdb0b 100644
--- a/reclass/output/__init__.py
+++ b/reclass/output/__init__.py
@@ -6,13 +6,15 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+
+
 class OutputterBase(object):
 
     def __init__(self):
         pass
 
     def dump(self, data, pretty_print=False):
-        raise NotImplementedError, "dump() method not yet implemented"
+        raise NotImplementedError('dump() method not implemented.')
 
 
 class OutputLoader(object):
@@ -27,6 +29,5 @@
     def load(self, attr='Outputter'):
         klass = getattr(self._module, attr, None)
         if klass is None:
-            raise AttributeError, \
-                'Outputter class {0} does not export "{1}"'.format(self._name, klass)
+            raise AttributeError('Outputter class {0} does not export "{1}"'.format(self._name, klass))
         return klass
diff --git a/reclass/output/json_outputter.py b/reclass/output/json_outputter.py
index dab86ed..8c79039 100644
--- a/reclass/output/json_outputter.py
+++ b/reclass/output/json_outputter.py
@@ -11,7 +11,7 @@
 
 class Outputter(OutputterBase):
 
-    def dump(self, data, pretty_print=False):
+    def dump(self, data, pretty_print=False, no_refs=False):
         separators = (',', ': ') if pretty_print else (',', ':')
         indent = 2 if pretty_print else None
         return json.dumps(data, indent=indent, separators=separators)
diff --git a/reclass/output/yaml_outputter.py b/reclass/output/yaml_outputter.py
index 2c70cc3..ef62979 100644
--- a/reclass/output/yaml_outputter.py
+++ b/reclass/output/yaml_outputter.py
@@ -9,7 +9,20 @@
 from reclass.output import OutputterBase
 import yaml
 
+_SafeDumper = yaml.CSafeDumper if yaml.__with_libyaml__ else yaml.SafeDumper
+
 class Outputter(OutputterBase):
 
-    def dump(self, data, pretty_print=False):
-        return yaml.dump(data, default_flow_style=not pretty_print)
+    def dump(self, data, pretty_print=False, no_refs=False):
+        if (no_refs):
+            return yaml.dump(data, default_flow_style=not pretty_print, Dumper=ExplicitDumper)
+        else:
+            return yaml.dump(data, default_flow_style=not pretty_print, Dumper=_SafeDumper)
+
+class ExplicitDumper(_SafeDumper):
+    """
+    A dumper that will never emit aliases.
+    """
+
+    def ignore_aliases(self, data):
+        return True
diff --git a/reclass/settings.py b/reclass/settings.py
new file mode 100644
index 0000000..e3fc26e
--- /dev/null
+++ b/reclass/settings.py
@@ -0,0 +1,68 @@
+import copy
+import reclass.values.parser_funcs
+from reclass.defaults import *
+
+try:
+    basestring
+except NameError:
+    basestring = str
+
+class Settings(object):
+
+    def __init__(self, options={}):
+        self.allow_scalar_over_dict = options.get('allow_scalar_over_dict', OPT_ALLOW_SCALAR_OVER_DICT)
+        self.allow_scalar_over_list = options.get('allow_scalar_over_list', OPT_ALLOW_SCALAR_OVER_LIST)
+        self.allow_list_over_scalar = options.get('allow_list_over_scalar', OPT_ALLOW_LIST_OVER_SCALAR)
+        self.allow_dict_over_scalar = options.get('allow_dict_over_scalar', OPT_ALLOW_DICT_OVER_SCALAR)
+        self.allow_none_override = options.get('allow_none_override', OPT_ALLOW_NONE_OVERRIDE)
+        self.automatic_parameters = options.get('automatic_parameters', AUTOMATIC_RECLASS_PARAMETERS)
+        self.default_environment = options.get('default_environment', DEFAULT_ENVIRONMENT)
+        self.delimiter = options.get('delimiter', PARAMETER_INTERPOLATION_DELIMITER)
+        self.dict_key_override_prefix = options.get('dict_key_override_prefix', PARAMETER_DICT_KEY_OVERRIDE_PREFIX)
+        self.escape_character = options.get('escape_character', ESCAPE_CHARACTER)
+        self.export_sentinels = options.get('export_sentinels', EXPORT_SENTINELS)
+        self.inventory_ignore_failed_node = options.get('inventory_ignore_failed_node', OPT_INVENTORY_IGNORE_FAILED_NODE)
+        self.inventory_ignore_failed_render = options.get('inventory_ignore_failed_render', OPT_INVENTORY_IGNORE_FAILED_RENDER)
+        self.reference_sentinels = options.get('reference_sentinels', REFERENCE_SENTINELS)
+        self.ignore_class_notfound = options.get('ignore_class_notfound', OPT_IGNORE_CLASS_NOTFOUND)
+
+        self.ignore_class_notfound_regexp = options.get('ignore_class_notfound_regexp', OPT_IGNORE_CLASS_NOTFOUND_REGEXP)
+        if isinstance(self.ignore_class_notfound_regexp, basestring):
+            self.ignore_class_notfound_regexp = [ self.ignore_class_notfound_regexp ]
+
+        self.ignore_class_notfound_warning = options.get('ignore_class_notfound_warning', OPT_IGNORE_CLASS_NOTFOUND_WARNING)
+        self.ignore_overwritten_missing_references = options.get('ignore_overwritten_missing_references', OPT_IGNORE_OVERWRITTEN_MISSING_REFERENCES)
+
+        self.group_errors = options.get('group_errors', OPT_GROUP_ERRORS)
+
+        self.ref_parser = reclass.values.parser_funcs.get_ref_parser(self.escape_character, self.reference_sentinels, self.export_sentinels)
+        self.simple_ref_parser = reclass.values.parser_funcs.get_simple_ref_parser(self.escape_character, self.reference_sentinels, self.export_sentinels)
+
+    def __eq__(self, other):
+        return isinstance(other, type(self)) \
+               and self.allow_scalar_over_dict == other.allow_scalar_over_dict \
+               and self.allow_scalar_over_list == other.allow_scalar_over_list \
+               and self.allow_list_over_scalar == other.allow_list_over_scalar \
+               and self.allow_dict_over_scalar == other.allow_dict_over_scalar \
+               and self.allow_none_override == other.allow_none_override \
+               and self.automatic_parameters == other.automatic_parameters \
+               and self.default_environment == other.default_environment \
+               and self.delimiter == other.delimiter \
+               and self.dict_key_override_prefix == other.dict_key_override_prefix \
+               and self.escape_character == other.escape_character \
+               and self.export_sentinels == other.export_sentinels \
+               and self.inventory_ignore_failed_node == other.inventory_ignore_failed_node \
+               and self.inventory_ignore_failed_render == other.inventory_ignore_failed_render \
+               and self.reference_sentinels == other.reference_sentinels \
+               and self.ignore_class_notfound == other.ignore_class_notfound \
+               and self.ignore_class_notfound_regexp == other.ignore_class_notfound_regexp \
+               and self.ignore_class_notfound_warning == other.ignore_class_notfound_warning
+
+    def __copy__(self):
+        cls = self.__class__
+        result = cls.__new__(cls)
+        result.__dict__.update(self.__dict__)
+        return result
+
+    def __deepcopy__(self, memo):
+        return self.__copy__()
diff --git a/reclass/storage/__init__.py b/reclass/storage/__init__.py
index 8ae2408..f49ac16 100644
--- a/reclass/storage/__init__.py
+++ b/reclass/storage/__init__.py
@@ -14,14 +14,18 @@
 
     name = property(lambda self: self._name)
 
-    def get_node(self, name, merge_base=None):
+    def get_node(self, name, settings):
         msg = "Storage class '{0}' does not implement node entity retrieval."
         raise NotImplementedError(msg.format(self.name))
 
-    def get_class(self, name):
+    def get_class(self, name, environment, settings):
         msg = "Storage class '{0}' does not implement class entity retrieval."
         raise NotImplementedError(msg.format(self.name))
 
     def enumerate_nodes(self):
         msg = "Storage class '{0}' does not implement node enumeration."
         raise NotImplementedError(msg.format(self.name))
+
+    def path_mangler(self):
+        msg = "Storage class '{0}' does not implement path_mangler."
+        raise NotImplementedError(msg.format(self.name))
diff --git a/reclass/storage/common.py b/reclass/storage/common.py
new file mode 100644
index 0000000..6a77fc8
--- /dev/null
+++ b/reclass/storage/common.py
@@ -0,0 +1,22 @@
+import os
+
+class NameMangler:
+    @staticmethod
+    def nodes(relpath, name):
+        # nodes are identified just by their basename, so
+        # no mangling required
+        return relpath, name
+
+    @staticmethod
+    def classes(relpath, name):
+        if relpath == '.' or relpath == '':
+            # './' is converted to None
+            return None, name
+        parts = relpath.split(os.path.sep)
+        if name != 'init':
+            # "init" is the directory index, so only append the basename
+            # to the path parts for all other filenames. This has the
+            # effect that data in file "foo/init.yml" will be registered
+            # as data for class "foo", not "foo.init"
+            parts.append(name)
+        return relpath, '.'.join(parts)
diff --git a/reclass/storage/loader.py b/reclass/storage/loader.py
index 399e7fd..10ca74c 100644
--- a/reclass/storage/loader.py
+++ b/reclass/storage/loader.py
@@ -6,13 +6,15 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+import importlib
+
 
 class StorageBackendLoader(object):
 
     def __init__(self, storage_name):
         self._name = 'reclass.storage.' + storage_name
         try:
-            self._module = __import__(self._name, globals(), locals(), self._name)
+            self._module = importlib.import_module(self._name)
         except ImportError:
             raise NotImplementedError
 
@@ -21,5 +23,10 @@
         if klass is None:
             raise AttributeError('Storage backend class {0} does not export '
                                  '"{1}"'.format(self._name, klassname))
-
         return klass
+
+    def path_mangler(self, name='path_mangler'):
+        function = getattr(self._module, name, None)
+        if function is None:
+            raise AttributeError('Storage backend class {0} does not export "{1}"'.format(self._name, name))
+        return function
diff --git a/reclass/storage/memcache_proxy.py b/reclass/storage/memcache_proxy.py
index 7d9ab5e..8c5e441 100644
--- a/reclass/storage/memcache_proxy.py
+++ b/reclass/storage/memcache_proxy.py
@@ -30,30 +30,27 @@
 
     name = property(lambda self: self._real_storage.name)
 
-    @staticmethod
-    def _cache_proxy(name, cache, getter):
+    def get_node(self, name, settings):
+        if not self._cache_nodes:
+            return self._real_storage.get_node(name, settings)
         try:
-            ret = cache[name]
-
-        except KeyError, e:
-            ret = getter(name)
-            cache[name] = ret
-
+            return self._nodes_cache[name]
+        except KeyError as e:
+            ret = self._real_storage.get_node(name, settings)
+            self._nodes_cache[name] = ret
         return ret
 
-    def get_node(self, name):
-        if not self._cache_nodes:
-            return self._real_storage.get_node(name)
-
-        return MemcacheProxy._cache_proxy(name, self._nodes_cache,
-                                          self._real_storage.get_node)
-
-    def get_class(self, name):
+    def get_class(self, name, environment, settings):
         if not self._cache_classes:
-            return self._real_storage.get_class(name)
-
-        return MemcacheProxy._cache_proxy(name, self._classes_cache,
-                                          self._real_storage.get_class)
+            return self._real_storage.get_class(name, environment, settings)
+        try:
+            return self._classes_cache[environment][name]
+        except KeyError as e:
+            if environment not in self._classes_cache:
+                self._classes_cache[environment] = dict()
+            ret = self._real_storage.get_class(name, environment, settings)
+            self._classes_cache[environment][name] = ret
+        return ret
 
     def enumerate_nodes(self):
         if not self._cache_nodelist:
diff --git a/reclass/storage/mixed/__init__.py b/reclass/storage/mixed/__init__.py
new file mode 100644
index 0000000..990c931
--- /dev/null
+++ b/reclass/storage/mixed/__init__.py
@@ -0,0 +1,60 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+
+import collections
+import copy
+
+from six import iteritems
+
+import reclass.errors
+from reclass import get_storage
+from reclass.storage import NodeStorageBase
+
+def path_mangler(inventory_base_uri, nodes_uri, classes_uri):
+    if nodes_uri == classes_uri:
+        raise errors.DuplicateUriError(nodes_uri, classes_uri)
+    return nodes_uri, classes_uri
+
+STORAGE_NAME = 'mixed'
+
+class ExternalNodeStorage(NodeStorageBase):
+
+    MixedUri = collections.namedtuple('MixedURI', 'storage_type options')
+
+    def __init__(self, nodes_uri, classes_uri):
+        super(ExternalNodeStorage, self).__init__(STORAGE_NAME)
+
+        self._nodes_uri = self._uri(nodes_uri)
+        self._nodes_storage = get_storage(self._nodes_uri.storage_type, self._nodes_uri.options, None)
+        self._classes_default_uri = self._uri(classes_uri)
+        self._classes_default_storage = get_storage(self._classes_default_uri.storage_type, None, self._classes_default_uri.options)
+
+        self._classes_storage = dict()
+        if 'env_overrides' in classes_uri:
+            for override in classes_uri['env_overrides']:
+                for (env, options) in iteritems(override):
+                        uri = copy.deepcopy(classes_uri)
+                        uri.update(options)
+                        uri = self._uri(uri)
+                        self._classes_storage[env] = get_storage(uri.storage_type, None, uri.options)
+
+    def _uri(self, uri):
+        ret = copy.deepcopy(uri)
+        ret['storage_type'] = uri['storage_type']
+        if 'env_overrides' in ret:
+            del ret['env_overrides']
+        if uri['storage_type'] == 'yaml_fs':
+            ret = ret['uri']
+        return self.MixedUri(uri['storage_type'], ret)
+
+    def get_node(self, name, settings):
+        return self._nodes_storage.get_node(name, settings)
+
+    def get_class(self, name, environment, settings):
+        storage = self._classes_storage.get(environment, self._classes_default_storage)
+        return storage.get_class(name, environment, settings)
+
+    def enumerate_nodes(self):
+        return self._nodes_storage.enumerate_nodes()
diff --git a/reclass/storage/tests/test_memcache_proxy.py b/reclass/storage/tests/test_memcache_proxy.py
index 066c27e..a47c29d 100644
--- a/reclass/storage/tests/test_memcache_proxy.py
+++ b/reclass/storage/tests/test_memcache_proxy.py
@@ -6,6 +6,8 @@
 # Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
 # Released under the terms of the Artistic Licence 2.0
 #
+
+from reclass.settings import Settings
 from reclass.storage.memcache_proxy import MemcacheProxy
 from reclass.storage import NodeStorageBase
 
@@ -22,48 +24,48 @@
 
     def test_no_nodes_caching(self):
         p = MemcacheProxy(self._storage, cache_nodes=False)
-        NAME = 'foo'; NAME2 = 'bar'; RET = 'baz'
+        NAME = 'foo'; NAME2 = 'bar'; RET = 'baz'; SETTINGS = Settings()
         self._storage.get_node.return_value = RET
-        self.assertEqual(p.get_node(NAME), RET)
-        self.assertEqual(p.get_node(NAME), RET)
-        self.assertEqual(p.get_node(NAME2), RET)
-        self.assertEqual(p.get_node(NAME2), RET)
-        expected = [mock.call(NAME), mock.call(NAME),
-                    mock.call(NAME2), mock.call(NAME2)]
+        self.assertEqual(p.get_node(NAME, SETTINGS), RET)
+        self.assertEqual(p.get_node(NAME, SETTINGS), RET)
+        self.assertEqual(p.get_node(NAME2, SETTINGS), RET)
+        self.assertEqual(p.get_node(NAME2, SETTINGS), RET)
+        expected = [mock.call(NAME, SETTINGS), mock.call(NAME, SETTINGS),
+                    mock.call(NAME2, SETTINGS), mock.call(NAME2, SETTINGS)]
         self.assertListEqual(self._storage.get_node.call_args_list, expected)
 
     def test_nodes_caching(self):
         p = MemcacheProxy(self._storage, cache_nodes=True)
-        NAME = 'foo'; NAME2 = 'bar'; RET = 'baz'
+        NAME = 'foo'; NAME2 = 'bar'; RET = 'baz'; SETTINGS = Settings()
         self._storage.get_node.return_value = RET
-        self.assertEqual(p.get_node(NAME), RET)
-        self.assertEqual(p.get_node(NAME), RET)
-        self.assertEqual(p.get_node(NAME2), RET)
-        self.assertEqual(p.get_node(NAME2), RET)
-        expected = [mock.call(NAME), mock.call(NAME2)] # called once each
+        self.assertEqual(p.get_node(NAME, SETTINGS), RET)
+        self.assertEqual(p.get_node(NAME, SETTINGS), RET)
+        self.assertEqual(p.get_node(NAME2, SETTINGS), RET)
+        self.assertEqual(p.get_node(NAME2, SETTINGS), RET)
+        expected = [mock.call(NAME, SETTINGS), mock.call(NAME2, SETTINGS)] # called once each
         self.assertListEqual(self._storage.get_node.call_args_list, expected)
 
     def test_no_classes_caching(self):
         p = MemcacheProxy(self._storage, cache_classes=False)
-        NAME = 'foo'; NAME2 = 'bar'; RET = 'baz'
+        NAME = 'foo'; NAME2 = 'bar'; RET = 'baz'; SETTINGS = Settings()
         self._storage.get_class.return_value = RET
-        self.assertEqual(p.get_class(NAME), RET)
-        self.assertEqual(p.get_class(NAME), RET)
-        self.assertEqual(p.get_class(NAME2), RET)
-        self.assertEqual(p.get_class(NAME2), RET)
-        expected = [mock.call(NAME), mock.call(NAME),
-                    mock.call(NAME2), mock.call(NAME2)]
+        self.assertEqual(p.get_class(NAME, None, SETTINGS), RET)
+        self.assertEqual(p.get_class(NAME, None, SETTINGS), RET)
+        self.assertEqual(p.get_class(NAME2, None, SETTINGS), RET)
+        self.assertEqual(p.get_class(NAME2, None, SETTINGS), RET)
+        expected = [mock.call(NAME, None, SETTINGS), mock.call(NAME, None, SETTINGS),
+                    mock.call(NAME2, None, SETTINGS), mock.call(NAME2, None, SETTINGS)]
         self.assertListEqual(self._storage.get_class.call_args_list, expected)
 
     def test_classes_caching(self):
         p = MemcacheProxy(self._storage, cache_classes=True)
-        NAME = 'foo'; NAME2 = 'bar'; RET = 'baz'
+        NAME = 'foo'; NAME2 = 'bar'; RET = 'baz'; SETTINGS = Settings()
         self._storage.get_class.return_value = RET
-        self.assertEqual(p.get_class(NAME), RET)
-        self.assertEqual(p.get_class(NAME), RET)
-        self.assertEqual(p.get_class(NAME2), RET)
-        self.assertEqual(p.get_class(NAME2), RET)
-        expected = [mock.call(NAME), mock.call(NAME2)] # called once each
+        self.assertEqual(p.get_class(NAME, None, SETTINGS), RET)
+        self.assertEqual(p.get_class(NAME, None, SETTINGS), RET)
+        self.assertEqual(p.get_class(NAME2, None, SETTINGS), RET)
+        self.assertEqual(p.get_class(NAME2, None, SETTINGS), RET)
+        expected = [mock.call(NAME, None, SETTINGS), mock.call(NAME2, None, SETTINGS)] # called once each
         self.assertListEqual(self._storage.get_class.call_args_list, expected)
 
     def test_nodelist_no_caching(self):
diff --git a/reclass/storage/tests/test_yamldata.py b/reclass/storage/tests/test_yamldata.py
new file mode 100644
index 0000000..d8129ce
--- /dev/null
+++ b/reclass/storage/tests/test_yamldata.py
@@ -0,0 +1,37 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass (http://github.com/madduck/reclass)
+#
+
+from reclass.storage.yamldata import YamlData
+
+import unittest
+
+class TestYamlData(unittest.TestCase):
+
+    def setUp(self):
+        lines = [ 'classes:',
+                  '  - testdir.test1',
+                  '  - testdir.test2',
+                  '  - test3',
+                  '',
+                  'environment: base',
+                  '',
+                  'parameters:',
+                  '  _TEST_:',
+                  '    alpha: 1',
+                  '    beta: two' ]
+        self.data = '\n'.join(lines)
+        self.yamldict = { 'classes': [ 'testdir.test1', 'testdir.test2', 'test3' ],
+                          'environment': 'base',
+                          'parameters': { '_TEST_': { 'alpha': 1, 'beta': 'two' } }
+                        }
+
+    def test_yaml_from_string(self):
+        res = YamlData.from_string(self.data, 'testpath')
+        self.assertEqual(res.uri, 'testpath')
+        self.assertEqual(res.get_data(), self.yamldict)
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/reclass/storage/yaml_fs/__init__.py b/reclass/storage/yaml_fs/__init__.py
index 5a13050..83f3666 100644
--- a/reclass/storage/yaml_fs/__init__.py
+++ b/reclass/storage/yaml_fs/__init__.py
@@ -8,9 +8,12 @@
 #
 import os, sys
 import fnmatch
+import yaml
+from reclass.output.yaml_outputter import ExplicitDumper
 from reclass.storage import NodeStorageBase
-from yamlfile import YamlFile
-from directory import Directory
+from reclass.storage.common import NameMangler
+from reclass.storage.yamldata import YamlData
+from .directory import Directory
 from reclass.datatypes import Entity
 import reclass.errors
 
@@ -21,34 +24,42 @@
     #print >>sys.stderr, msg
     pass
 
+def path_mangler(inventory_base_uri, nodes_uri, classes_uri):
+
+    if inventory_base_uri is None:
+        # if inventory_base is not given, default to current directory
+        inventory_base_uri = os.getcwd()
+
+    nodes_uri = nodes_uri or 'nodes'
+    classes_uri = classes_uri or 'classes'
+
+    def _path_mangler_inner(path):
+        ret = os.path.join(inventory_base_uri, path)
+        ret = os.path.expanduser(ret)
+        return os.path.abspath(ret)
+
+    n, c = map(_path_mangler_inner, (nodes_uri, classes_uri))
+    if n == c:
+        raise errors.DuplicateUriError(n, c)
+    common = os.path.commonprefix((n, c))
+    if common == n or common == c:
+        raise errors.UriOverlapError(n, c)
+
+    return n, c
+
+
 class ExternalNodeStorage(NodeStorageBase):
 
-    def __init__(self, nodes_uri, classes_uri, default_environment=None):
+    def __init__(self, nodes_uri, classes_uri):
         super(ExternalNodeStorage, self).__init__(STORAGE_NAME)
 
-        def name_mangler(relpath, name):
-            # nodes are identified just by their basename, so
-            # no mangling required
-            return relpath, name
-        self._nodes_uri = nodes_uri
-        self._nodes = self._enumerate_inventory(nodes_uri, name_mangler)
+        if nodes_uri is not None:
+            self._nodes_uri = nodes_uri
+            self._nodes = self._enumerate_inventory(nodes_uri, NameMangler.nodes)
 
-        def name_mangler(relpath, name):
-            if relpath == '.':
-                # './' is converted to None
-                return None, name
-            parts = relpath.split(os.path.sep)
-            if name != 'init':
-                # "init" is the directory index, so only append the basename
-                # to the path parts for all other filenames. This has the
-                # effect that data in file "foo/init.yml" will be registered
-                # as data for class "foo", not "foo.init"
-                parts.append(name)
-            return relpath, '.'.join(parts)
-        self._classes_uri = classes_uri
-        self._classes = self._enumerate_inventory(classes_uri, name_mangler)
-
-        self._default_environment = default_environment
+        if classes_uri is not None:
+            self._classes_uri = classes_uri
+            self._classes = self._enumerate_inventory(classes_uri, NameMangler.classes)
 
     nodes_uri = property(lambda self: self._nodes_uri)
     classes_uri = property(lambda self: self._classes_uri)
@@ -76,24 +87,24 @@
         d.walk(register_fn)
         return ret
 
-    def get_node(self, name):
+    def get_node(self, name, settings):
         vvv('GET NODE {0}'.format(name))
         try:
             relpath = self._nodes[name]
             path = os.path.join(self.nodes_uri, relpath)
             name = os.path.splitext(relpath)[0]
-        except KeyError, e:
+        except KeyError as e:
             raise reclass.errors.NodeNotFound(self.name, name, self.nodes_uri)
-        entity = YamlFile(path).get_entity(name, self._default_environment)
+        entity = YamlData.from_file(path).get_entity(name, settings)
         return entity
 
-    def get_class(self, name, nodename=None):
+    def get_class(self, name, environment, settings):
         vvv('GET CLASS {0}'.format(name))
         try:
             path = os.path.join(self.classes_uri, self._classes[name])
-        except KeyError, e:
+        except KeyError as e:
             raise reclass.errors.ClassNotFound(self.name, name, self.classes_uri)
-        entity = YamlFile(path).get_entity(name)
+        entity = YamlData.from_file(path).get_entity(name, settings)
         return entity
 
     def enumerate_nodes(self):
diff --git a/reclass/storage/yaml_fs/directory.py b/reclass/storage/yaml_fs/directory.py
index 03302b7..614e1c3 100644
--- a/reclass/storage/yaml_fs/directory.py
+++ b/reclass/storage/yaml_fs/directory.py
@@ -7,16 +7,16 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 import os
-import sys
 from reclass.errors import NotFoundError
 
-SKIPDIRS = ( 'CVS', 'SCCS' )
+SKIPDIRS = ('CVS', 'SCCS')
 FILE_EXTENSION = '.yml'
 
 def vvv(msg):
     #print >>sys.stderr, msg
     pass
 
+
 class Directory(object):
 
     def __init__(self, path, fileclass=None):
@@ -39,7 +39,8 @@
     files = property(lambda self: self._files)
 
     def walk(self, register_fn=None):
-        if not callable(register_fn): register_fn = self._register_files
+        if not callable(register_fn):
+            register_fn = self._register_files
 
         def _error(exc):
             raise(exc)
diff --git a/reclass/storage/yaml_fs/yamlfile.py b/reclass/storage/yaml_fs/yamlfile.py
deleted file mode 100644
index 717a911..0000000
--- a/reclass/storage/yaml_fs/yamlfile.py
+++ /dev/null
@@ -1,61 +0,0 @@
-#
-# -*- coding: utf-8 -*-
-#
-# This file is part of reclass (http://github.com/madduck/reclass)
-#
-# Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
-# Released under the terms of the Artistic Licence 2.0
-#
-from reclass import datatypes
-import yaml
-import os
-from reclass.errors import NotFoundError
-
-class YamlFile(object):
-
-    def __init__(self, path):
-        ''' Initialise a yamlfile object '''
-        if not os.path.isfile(path):
-            raise NotFoundError('No such file: %s' % path)
-        if not os.access(path, os.R_OK):
-            raise NotFoundError('Cannot open: %s' % path)
-        self._path = path
-        self._data = dict()
-        self._read()
-    path = property(lambda self: self._path)
-
-    def _read(self):
-        fp = file(self._path)
-        data = yaml.safe_load(fp)
-        if data is not None:
-            self._data = data
-        fp.close()
-
-    def get_entity(self, name=None, default_environment=None):
-        classes = self._data.get('classes')
-        if classes is None:
-            classes = []
-        classes = datatypes.Classes(classes)
-
-        applications = self._data.get('applications')
-        if applications is None:
-            applications = []
-        applications = datatypes.Applications(applications)
-
-        parameters = self._data.get('parameters')
-        if parameters is None:
-            parameters = {}
-        parameters = datatypes.Parameters(parameters)
-
-        env = self._data.get('environment', default_environment)
-
-        if name is None:
-            name = self._path
-
-        return datatypes.Entity(classes, applications, parameters,
-                                name=name, environment=env,
-                                uri='yaml_fs://{0}'.format(self._path))
-
-    def __repr__(self):
-        return '<{0} {1}, {2}>'.format(self.__class__.__name__, self._path,
-                                       self._data.keys())
diff --git a/reclass/storage/yaml_git/__init__.py b/reclass/storage/yaml_git/__init__.py
new file mode 100644
index 0000000..86c1247
--- /dev/null
+++ b/reclass/storage/yaml_git/__init__.py
@@ -0,0 +1,269 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+
+import collections
+import distutils.version
+import fnmatch
+import os
+
+# Squelch warning on centos7 due to upgrading cffi
+# see https://github.com/saltstack/salt/pull/39871
+import warnings
+with warnings.catch_warnings():
+    warnings.simplefilter('ignore')
+    import pygit2
+
+from six import iteritems
+
+import reclass.errors
+from reclass.storage import NodeStorageBase
+from reclass.storage.common import NameMangler
+from reclass.storage.yamldata import YamlData
+
+FILE_EXTENSION = '.yml'
+STORAGE_NAME = 'yaml_git'
+
+def path_mangler(inventory_base_uri, nodes_uri, classes_uri):
+    if nodes_uri == classes_uri:
+        raise errors.DuplicateUriError(nodes_uri, classes_uri)
+    return nodes_uri, classes_uri
+
+
+GitMD = collections.namedtuple('GitMD', ['name', 'path', 'id'], verbose=False, rename=False)
+
+
+class GitURI(object):
+
+    def __init__(self, dictionary):
+        self.repo = None
+        self.branch = None
+        self.root = None
+        self.cache_dir = None
+        self.pubkey = None
+        self.privkey = None
+        self.password = None
+        self.update(dictionary)
+
+    def update(self, dictionary):
+        if 'repo' in dictionary: self.repo = dictionary['repo']
+        if 'branch' in dictionary: self.branch = dictionary['branch']
+        if 'cache_dir' in dictionary: self.cache_dir = dictionary['cache_dir']
+        if 'pubkey' in dictionary: self.pubkey = dictionary['pubkey']
+        if 'privkey' in dictionary: self.privkey = dictionary['privkey']
+        if 'password' in dictionary: self.password = dictionary['password']
+        if 'root' in dictionary:
+            if dictionary['root'] is None:
+                self.root = None
+            else:
+                self.root = dictionary['root'].replace('/', '.')
+
+    def __repr__(self):
+        return '<{0}: {1} {2} {3}>'.format(self.__class__.__name__, self.repo, self.branch, self.root)
+
+
+class GitRepo(object):
+
+    def __init__(self, uri):
+        self.transport, _, self.url = uri.repo.partition('://')
+        self.name = self.url.replace('/', '_')
+        self.credentials = None
+        self.remotecallbacks = None
+        if uri.cache_dir is None:
+            self.cache_dir = '{0}/{1}/{2}'.format(os.path.expanduser("~"), '.reclass/cache/git', self.name)
+        else:
+            self.cache_dir = '{0}/{1}'.format(uri.cache_dir, self.name)
+
+        self._init_repo(uri)
+        self._fetch()
+        self.branches = self.repo.listall_branches()
+        self.files = self.files_in_repo()
+
+    def _init_repo(self, uri):
+        if os.path.exists(self.cache_dir):
+            self.repo = pygit2.Repository(self.cache_dir)
+        else:
+            os.makedirs(self.cache_dir)
+            self.repo = pygit2.init_repository(self.cache_dir, bare=True)
+
+        if not self.repo.remotes:
+            self.repo.create_remote('origin', self.url)
+
+        if 'ssh' in self.transport:
+            if '@' in self.url:
+                user, _, _ = self.url.partition('@')
+            else:
+                user = 'gitlab'
+
+            if uri.pubkey is not None:
+                creds = pygit2.Keypair(user, uri.pubkey, uri.privkey, uri.password)
+            else:
+                creds = pygit2.KeypairFromAgent(user)
+
+            pygit2_version = pygit2.__version__
+            if distutils.version.LooseVersion(pygit2_version) >= distutils.version.LooseVersion('0.23.2'):
+                self.remotecallbacks = pygit2.RemoteCallbacks(credentials=creds)
+                self.credentials = None
+            else:
+                self.remotecallbacks = None
+                self.credentials = creds
+
+    def _fetch(self):
+        origin = self.repo.remotes[0]
+        fetch_kwargs = {}
+        if self.remotecallbacks is not None:
+            fetch_kwargs['callbacks'] = self.remotecallbacks
+        if self.credentials is not None:
+            origin.credentials = self.credentials
+        fetch_results = origin.fetch(**fetch_kwargs)
+
+        remote_branches = self.repo.listall_branches(pygit2.GIT_BRANCH_REMOTE)
+        local_branches = self.repo.listall_branches()
+        for remote_branch_name in remote_branches:
+            _, _, local_branch_name = remote_branch_name.partition('/')
+            remote_branch = self.repo.lookup_branch(remote_branch_name, pygit2.GIT_BRANCH_REMOTE)
+            if local_branch_name not in local_branches:
+                local_branch = self.repo.create_branch(local_branch_name, self.repo[remote_branch.target.hex])
+                local_branch.upstream = remote_branch
+            else:
+                local_branch = self.repo.lookup_branch(local_branch_name)
+                if local_branch.target != remote_branch.target:
+                    local_branch.set_target(remote_branch.target)
+
+        local_branches = self.repo.listall_branches()
+        for local_branch_name in local_branches:
+            remote_branch_name = '{0}/{1}'.format(origin.name, local_branch_name)
+            if remote_branch_name not in remote_branches:
+                local_branch = self.repo.lookup_branch(local_branch_name)
+                local.branch.delete()
+
+    def get(self, id):
+        return self.repo.get(id)
+
+    def files_in_tree(self, tree, path):
+        files = []
+        for entry in tree:
+            if entry.filemode == pygit2.GIT_FILEMODE_TREE:
+                subtree = self.repo.get(entry.id)
+                if path == '':
+                    subpath = entry.name
+                else:
+                    subpath = '/'.join([path, entry.name])
+                files.extend(self.files_in_tree(subtree, subpath))
+            else:
+                if path == '':
+                   relpath = entry.name
+                else:
+                   relpath = '/'.join([path, entry.name])
+                files.append(GitMD(entry.name, relpath, entry.id))
+        return files
+
+    def files_in_branch(self, branch):
+        tree = self.repo.revparse_single(branch).tree
+        return self.files_in_tree(tree, '')
+
+    def files_in_repo(self):
+        ret = {}
+        for bname in self.branches:
+            branch = {}
+            files = self.files_in_branch(bname)
+            for file in files:
+                if fnmatch.fnmatch(file.name, '*{0}'.format(FILE_EXTENSION)):
+                    name = os.path.splitext(file.name)[0]
+                    relpath = os.path.dirname(file.path)
+                    relpath, name = NameMangler.classes(relpath, name)
+                    if name in ret:
+                        raise reclass.errors.DuplicateNodeNameError(self.name + ' - ' + bname, name, ret[name], path)
+                    else:
+                        branch[name] = file
+            ret[bname] = branch
+        return ret
+
+    def nodes(self, branch, subdir):
+        ret = {}
+        for (name, file) in iteritems(self.files[branch]):
+            if subdir is None or name.startswith(subdir):
+                node_name = os.path.splitext(file.name)[0]
+                if node_name in ret:
+                    raise reclass.errors.DuplicateNodeNameError(self.name, name, files[name], path)
+                else:
+                    ret[node_name] = file
+        return ret
+
+class ExternalNodeStorage(NodeStorageBase):
+
+    def __init__(self, nodes_uri, classes_uri):
+        super(ExternalNodeStorage, self).__init__(STORAGE_NAME)
+        self._repos = dict()
+
+        if nodes_uri is not None:
+            self._nodes_uri = GitURI({ 'branch': 'master' })
+            self._nodes_uri.update(nodes_uri)
+            self._load_repo(self._nodes_uri)
+            self._nodes = self._repos[self._nodes_uri.repo].nodes(self._nodes_uri.branch, self._nodes_uri.root)
+
+        if classes_uri is not None:
+            self._classes_default_uri = GitURI({ 'branch': '__env__' })
+            self._classes_default_uri.update(classes_uri)
+            self._load_repo(self._classes_default_uri)
+
+            self._classes_uri = []
+            if 'env_overrides' in classes_uri:
+                for override in classes_uri['env_overrides']:
+                    for (env, options) in iteritems(override):
+                        uri = GitURI(self._classes_default_uri)
+                        uri.update({ 'branch': env })
+                        uri.update(options)
+                        self._classes_uri.append((env, uri))
+                        self._load_repo(uri)
+
+            self._classes_uri.append(('*', self._classes_default_uri))
+
+    nodes_uri = property(lambda self: self._nodes_uri)
+    classes_uri = property(lambda self: self._classes_uri)
+
+    def get_node(self, name, settings):
+        file = self._nodes[name]
+        blob = self._repos[self._nodes_uri.repo].get(file.id)
+        entity = YamlData.from_string(blob.data, 'git_fs://{0} {1} {2}'.format(self._nodes_uri.repo, self._nodes_uri.branch, file.path)).get_entity(name, settings)
+        return entity
+
+    def get_class(self, name, environment, settings):
+        uri = self._env_to_uri(environment)
+        if uri.root is not None:
+            name = '{0}.{1}'.format(uri.root, name)
+        if uri.repo not in self._repos:
+            raise reclass.errors.NotFoundError("Repo " + uri.repo + " unknown or missing")
+        if uri.branch not in self._repos[uri.repo].files:
+            raise reclass.errors.NotFoundError("Branch " + uri.branch + " missing from " + uri.repo)
+        if name not in self._repos[uri.repo].files[uri.branch]:
+            raise reclass.errors.NotFoundError("File " + name + " missing from " + uri.repo + " branch " + uri.branch)
+        file = self._repos[uri.repo].files[uri.branch][name]
+        blob = self._repos[uri.repo].get(file.id)
+        entity = YamlData.from_string(blob.data, 'git_fs://{0} {1} {2}'.format(uri.repo, uri.branch, file.path)).get_entity(name, settings)
+        return entity
+
+    def enumerate_nodes(self):
+        return self._nodes.keys()
+
+    def _load_repo(self, uri):
+        if uri.repo not in self._repos:
+            self._repos[uri.repo] = GitRepo(uri)
+
+    def _env_to_uri(self, environment):
+        ret = None
+        if environment is None:
+            ret = self._classes_default_uri
+        else:
+            for env, uri in self._classes_uri:
+                if env == environment:
+                    ret = uri
+                    break
+        if ret is None:
+            ret = self._classes_default_uri
+        if ret.branch == '__env__':
+            ret.branch = environment
+        if ret.branch == None:
+            ret.branch = 'master'
+        return ret
diff --git a/reclass/storage/yamldata.py b/reclass/storage/yamldata.py
new file mode 100644
index 0000000..b11312e
--- /dev/null
+++ b/reclass/storage/yamldata.py
@@ -0,0 +1,86 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass (http://github.com/madduck/reclass)
+#
+# Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
+# Released under the terms of the Artistic Licence 2.0
+#
+from reclass import datatypes
+import yaml
+import os
+from reclass.errors import NotFoundError
+
+_SafeLoader = yaml.CSafeLoader if yaml.__with_libyaml__ else yaml.SafeLoader
+
+class YamlData(object):
+
+    @classmethod
+    def from_file(cls, path):
+        ''' Initialise yaml data from a local file '''
+        abs_path = os.path.abspath(path)
+        if not os.path.isfile(abs_path):
+            raise NotFoundError('No such file: %s' % abs_path)
+        if not os.access(abs_path, os.R_OK):
+            raise NotFoundError('Cannot open: %s' % abs_path)
+        y = cls('yaml_fs://{0}'.format(abs_path))
+        with open(abs_path) as fp:
+            data = yaml.load(fp, Loader=_SafeLoader)
+            if data is not None:
+                y._data = data
+        return y
+
+    @classmethod
+    def from_string(cls, string, uri):
+        ''' Initialise yaml data from a string '''
+        y = cls(uri)
+        data = yaml.load(string, Loader=_SafeLoader)
+        if data is not None:
+            y._data = data
+        return y
+
+    def __init__(self, uri):
+        self._uri = uri
+        self._data = dict()
+
+    uri = property(lambda self: self._uri)
+
+    def get_data(self):
+        return self._data
+
+    def get_entity(self, name, settings):
+        #if name is None:
+        #    name = self._uri
+
+        classes = self._data.get('classes')
+        if classes is None:
+            classes = []
+        classes = datatypes.Classes(classes)
+
+        applications = self._data.get('applications')
+        if applications is None:
+            applications = []
+        applications = datatypes.Applications(applications)
+
+        parameters = self._data.get('parameters')
+        if parameters is None:
+            parameters = {}
+        parameters = datatypes.Parameters(parameters, settings, self._uri)
+
+        exports = self._data.get('exports')
+        if exports is None:
+            exports = {}
+        exports = datatypes.Exports(exports, settings, self._uri)
+
+        env = self._data.get('environment', None)
+
+        return datatypes.Entity(settings, classes=classes, applications=applications, parameters=parameters,
+                                exports=exports, name=name, environment=env, uri=self.uri)
+
+    def __str__(self):
+        return '<{0} {1}, {2}>'.format(self.__class__.__name__, self._uri,
+                                       self._data)
+
+    def __repr__(self):
+        return '<{0} {1}, {2}>'.format(self.__class__.__name__, self._uri,
+                                       self._data.keys())
diff --git a/reclass/tests/__init__.py b/reclass/tests/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/reclass/tests/__init__.py
diff --git a/reclass/tests/data/01/classes/standard.yml b/reclass/tests/data/01/classes/standard.yml
new file mode 100644
index 0000000..13bce54
--- /dev/null
+++ b/reclass/tests/data/01/classes/standard.yml
@@ -0,0 +1,4 @@
+parameters:
+  int: 1
+  string: '1'
+  bool: True
diff --git a/reclass/tests/data/01/nodes/class_notfound.yml b/reclass/tests/data/01/nodes/class_notfound.yml
new file mode 100644
index 0000000..616a49b
--- /dev/null
+++ b/reclass/tests/data/01/nodes/class_notfound.yml
@@ -0,0 +1,5 @@
+classes:
+  - missing
+
+parameters:
+  node_test: class not found
diff --git a/reclass/tests/data/01/nodes/data_types.yml b/reclass/tests/data/01/nodes/data_types.yml
new file mode 100644
index 0000000..28ff151
--- /dev/null
+++ b/reclass/tests/data/01/nodes/data_types.yml
@@ -0,0 +1,2 @@
+classes:
+  - standard
diff --git a/reclass/tests/test_core.py b/reclass/tests/test_core.py
new file mode 100644
index 0000000..9225756
--- /dev/null
+++ b/reclass/tests/test_core.py
@@ -0,0 +1,60 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass (http://github.com/madduck/reclass)
+#
+
+import os
+
+from reclass import get_storage, get_path_mangler
+from reclass.core import Core
+from reclass.settings import Settings
+from reclass.errors import ClassNotFound
+
+import unittest
+try:
+    import unittest.mock as mock
+except ImportError:
+    import mock
+
+class TestCore(unittest.TestCase):
+
+    def _core(self, dataset, opts={}):
+        inventory_uri = os.path.dirname(os.path.abspath(__file__)) + '/data/' + dataset
+        path_mangler = get_path_mangler('yaml_fs')
+        nodes_uri, classes_uri = path_mangler(inventory_uri, 'nodes', 'classes')
+        storage = get_storage('yaml_fs', nodes_uri, classes_uri)
+        settings = Settings(opts)
+        return Core(storage, None, settings)
+
+    def test_type_conversion(self):
+        reclass = self._core('01')
+        node = reclass.nodeinfo('data_types')
+        params = { 'int': 1, 'bool': True, 'string': '1', '_reclass_': { 'environment': 'base', 'name': {'full': 'data_types', 'short': 'data_types' } } }
+        self.assertEqual(node['parameters'], params)
+
+    def test_raise_class_notfound(self):
+        reclass = self._core('01')
+        with self.assertRaises(ClassNotFound):
+            node = reclass.nodeinfo('class_notfound')
+
+    def test_ignore_class_notfound(self):
+        reclass = self._core('01', opts={ 'ignore_class_notfound': True, 'ignore_class_notfound_warning': False })
+        node = reclass.nodeinfo('class_notfound')
+        params = { 'node_test': 'class not found', '_reclass_': { 'environment': 'base', 'name': {'full': 'class_notfound', 'short': 'class_notfound' } } }
+        self.assertEqual(node['parameters'], params)
+
+    def test_raise_class_notfound_with_regexp(self):
+        reclass = self._core('01', opts={ 'ignore_class_notfound': True, 'ignore_class_notfound_warning': False, 'ignore_class_notfound_regexp': 'notmatched.*' })
+        with self.assertRaises(ClassNotFound):
+            node = reclass.nodeinfo('class_notfound')
+
+    def test_ignore_class_notfound_with_regexp(self):
+        reclass = self._core('01', opts={ 'ignore_class_notfound': True, 'ignore_class_notfound_warning': False, 'ignore_class_notfound_regexp': 'miss.*' })
+        node = reclass.nodeinfo('class_notfound')
+        params = { 'node_test': 'class not found', '_reclass_': { 'environment': 'base', 'name': {'full': 'class_notfound', 'short': 'class_notfound' } } }
+        self.assertEqual(node['parameters'], params)
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/reclass/utils/dictpath.py b/reclass/utils/dictpath.py
index db95e66..dfb8b32 100644
--- a/reclass/utils/dictpath.py
+++ b/reclass/utils/dictpath.py
@@ -7,7 +7,8 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 
-import types, re
+import six
+import re
 
 class DictPath(object):
     '''
@@ -59,12 +60,12 @@
         if contents is None:
             self._parts = []
         else:
-            if isinstance(contents, types.StringTypes):
+            if isinstance(contents, list):
+                self._parts = contents
+            elif isinstance(contents, six.string_types):
                 self._parts = self._split_string(contents)
             elif isinstance(contents, tuple):
                 self._parts = list(contents)
-            elif isinstance(contents, list):
-                self._parts = contents
             else:
                 raise TypeError('DictPath() takes string or list, '\
                                 'not %s' % type(contents))
@@ -76,7 +77,7 @@
         return self._delim.join(str(i) for i in self._parts)
 
     def __eq__(self, other):
-        if isinstance(other, types.StringTypes):
+        if isinstance(other, six.string_types):
             other = DictPath(self._delim, other)
 
         return self._parts == other._parts \
@@ -112,14 +113,59 @@
     def _escape_string(self, string):
         return string.replace(self._delim, '\\' + self._delim)
 
+    def has_ancestors(self):
+        return len(self._parts) > 1
+
+    def key_parts(self):
+        if self.has_ancestors():
+            return self._parts[:-1]
+        else:
+            return []
+
     def new_subpath(self, key):
-        try:
-            return DictPath(self._delim, self._parts + [self._escape_string(key)])
-        except AttributeError as e:
-            return DictPath(self._delim, self._parts + [key])
+        return DictPath(self._delim, self._parts + [key])
 
     def get_value(self, base):
         return self._get_innermost_container(base)[self._get_key()]
 
     def set_value(self, base, value):
         self._get_innermost_container(base)[self._get_key()] = value
+
+    def drop_first(self):
+        del self._parts[0]
+        return self
+
+    def is_empty(self):
+        return len(self._parts) == 0
+
+    def delete(self, base):
+        del self._get_innermost_container(base)[self._get_key()]
+
+    def add_subpath(self, key):
+        self._parts.append(key)
+
+    def is_ancestor_of(self, other):
+        if len(other._parts) <= len(self._parts):
+            return False
+        for i in range(len(self._parts)):
+            if other._parts[i] != self._parts[i]:
+                return False
+        return True
+
+    def exists_in(self, container):
+        item = container
+        for i in self._parts:
+            if isinstance(item, (dict, list)):
+                if i in item:
+                    if isinstance(item, dict):
+                        item = item[i]
+                    elif isinstance(container, list):
+                        item = item[int(i)]
+                else:
+                    return False
+            else:
+                if item == self._parts[-1]:
+                    return True
+                else:
+                    return False
+        return True
diff --git a/reclass/utils/refvalue.py b/reclass/utils/refvalue.py
deleted file mode 100644
index b8e730b..0000000
--- a/reclass/utils/refvalue.py
+++ /dev/null
@@ -1,115 +0,0 @@
-#
-# -*- coding: utf-8 -*-
-#
-# This file is part of reclass (http://github.com/madduck/reclass)
-#
-# Copyright © 2007–14 martin f. krafft <madduck@madduck.net>
-# Released under the terms of the Artistic Licence 2.0
-#
-
-import re
-
-from reclass.utils.dictpath import DictPath
-from reclass.defaults import PARAMETER_INTERPOLATION_SENTINELS, \
-        PARAMETER_INTERPOLATION_DELIMITER
-from reclass.errors import IncompleteInterpolationError, \
-        UndefinedVariableError
-
-_SENTINELS = [re.escape(s) for s in PARAMETER_INTERPOLATION_SENTINELS]
-_RE = '{0}\s*(.+?)\s*{1}'.format(*_SENTINELS)
-
-class RefValue(object):
-    '''
-    Isolates references in string values
-
-    RefValue can be used to isolate and eventually expand references to other
-    parameters in strings. Those references can then be iterated and rendered
-    in the context of a dictionary to resolve those references.
-
-    RefValue always gets constructed from a string, because templating
-    — essentially this is what's going on — is necessarily always about
-    strings. Therefore, generally, the rendered value of a RefValue instance
-    will also be a string.
-
-    Nevertheless, as this might not be desirable, RefValue will return the
-    referenced variable without casting it to a string, if the templated
-    string contains nothing but the reference itself.
-
-    For instance:
-
-      mydict = {'favcolour': 'yellow', 'answer': 42, 'list': [1,2,3]}
-      RefValue('My favourite colour is ${favolour}').render(mydict)
-      → 'My favourite colour is yellow'      # a string
-
-      RefValue('The answer is ${answer}').render(mydict)
-      → 'The answer is 42'                   # a string
-
-      RefValue('${answer}').render(mydict)
-      → 42                                   # an int
-
-      RefValue('${list}').render(mydict)
-      → [1,2,3]                              # an list
-
-    The markers used to identify references are set in reclass.defaults, as is
-    the default delimiter.
-    '''
-
-    INTERPOLATION_RE = re.compile(_RE)
-
-    def __init__(self, string, delim=PARAMETER_INTERPOLATION_DELIMITER):
-        self._strings = []
-        self._refs = []
-        self._delim = delim
-        self._parse(string)
-
-    def _parse(self, string):
-        parts = RefValue.INTERPOLATION_RE.split(string)
-        self._refs = parts[1:][::2]
-        self._strings = parts[0:][::2]
-        self._check_strings(string)
-
-    def _check_strings(self, orig):
-        for s in self._strings:
-            pos = s.find(PARAMETER_INTERPOLATION_SENTINELS[0])
-            if pos >= 0:
-                raise IncompleteInterpolationError(orig,
-                                                   PARAMETER_INTERPOLATION_SENTINELS[1])
-
-    def _resolve(self, ref, context):
-        path = DictPath(self._delim, ref)
-        try:
-            return path.get_value(context)
-        except KeyError as e:
-            raise UndefinedVariableError(ref)
-
-    def has_references(self):
-        return len(self._refs) > 0
-
-    def get_references(self):
-        return self._refs
-
-    def _assemble(self, resolver):
-        if not self.has_references():
-            return self._strings[0]
-
-        if self._strings == ['', '']:
-            # preserve the type of the referenced variable
-            return resolver(self._refs[0])
-
-        # reassemble the string by taking a string and str(ref) pairwise
-        ret = ''
-        for i in range(0, len(self._refs)):
-            ret += self._strings[i] + str(resolver(self._refs[i]))
-        if len(self._strings) > len(self._refs):
-            # and finally append a trailing string, if any
-            ret += self._strings[-1]
-        return ret
-
-    def render(self, context):
-        resolver = lambda s: self._resolve(s, context)
-        return self._assemble(resolver)
-
-    def __repr__(self):
-        do_not_resolve = lambda s: s.join(PARAMETER_INTERPOLATION_SENTINELS)
-        return 'RefValue(%r, %r)' % (self._assemble(do_not_resolve),
-                                     self._delim)
diff --git a/reclass/values/__init__.py b/reclass/values/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/reclass/values/__init__.py
diff --git a/reclass/values/compitem.py b/reclass/values/compitem.py
new file mode 100644
index 0000000..c6e8863
--- /dev/null
+++ b/reclass/values/compitem.py
@@ -0,0 +1,69 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+from reclass.settings import Settings
+from .item import Item
+
+class CompItem(Item):
+
+    def __init__(self, items, settings):
+        self.type = Item.COMPOSITE
+        self._items = items
+        self._settings = settings
+        self._refs = []
+        self._allRefs = False
+        self.assembleRefs()
+
+    def assembleRefs(self, context={}):
+        self._refs = []
+        self._allRefs = True
+        for item in self._items:
+            if item.has_references():
+                item.assembleRefs(context)
+                self._refs.extend(item.get_references())
+                if item.allRefs() is False:
+                    self._allRefs = False
+
+    def contents(self):
+        return self._items
+
+    def allRefs(self):
+        return self._allRefs
+
+    def has_references(self):
+        return len(self._refs) > 0
+
+    def get_references(self):
+        return self._refs
+
+    def merge_over(self, item):
+        if item.type == Item.SCALAR or item.type == Item.COMPOSITE:
+            return self
+        elif item.type == Item.LIST:
+            if self._settings.allow_scalar_over_list or (self._settings.allow_none_override and self._value in [None, 'none', 'None']):
+                return self
+            else:
+                raise TypeError('allow scalar over list = False: cannot merge %s over %s' % (repr(self), repr(item)))
+        elif item.type == Item.DICTIONARY:
+            if self._settings.allow_scalar_over_dict or (self._settings.allow_none_override and self._value in [None, 'none', 'None']):
+                return self
+            else:
+                raise TypeError('allow scalar over dict = False: cannot merge %s over %s' % (repr(self), repr(item)))
+        raise TypeError('Cannot merge %s over %s' % (repr(self), repr(item)))
+
+    def render(self, context, inventory):
+        # Preserve type if only one item
+        if len(self._items) == 1:
+            return self._items[0].render(context, inventory)
+        # Multiple items
+        strings = [ str(i.render(context, inventory)) for i in self._items ]
+        return "".join(strings)
+
+    def __repr__(self):
+        return 'CompItem(%r)' % self._items
+
+    def __str__(self):
+        return ''.join([ str(i) for i in self._items ])
diff --git a/reclass/values/dictitem.py b/reclass/values/dictitem.py
new file mode 100644
index 0000000..555bd8f
--- /dev/null
+++ b/reclass/values/dictitem.py
@@ -0,0 +1,35 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+from reclass.settings import Settings
+from .item import Item
+
+class DictItem(Item):
+
+    def __init__(self, item, settings):
+        self.type = Item.DICTIONARY
+        self._dict = item
+        self._settings = settings
+
+    def contents(self):
+        return self._dict
+
+    def is_container(self):
+        return True
+
+    def merge_over(self, item):
+        if item.type == Item.SCALAR:
+            if item.contents() is None or self._settings.allow_dict_over_scalar:
+                return self
+            else:
+                raise TypeError('allow dict over scalar = False: cannot merge %s onto %s' % (repr(self), repr(item)))
+        raise TypeError('Cannot merge %s over %s' % (repr(self), repr(item)))
+
+    def render(self, context, inventory):
+        return self._dict
+
+    def __repr__(self):
+        return 'DictItem(%r)' % self._dict
diff --git a/reclass/values/invitem.py b/reclass/values/invitem.py
new file mode 100644
index 0000000..970321b
--- /dev/null
+++ b/reclass/values/invitem.py
@@ -0,0 +1,341 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+import copy
+import pyparsing as pp
+
+from six import iteritems
+
+from .item import Item
+from reclass.settings import Settings
+from reclass.utils.dictpath import DictPath
+from reclass.errors import ExpressionError, ParseError, ResolveError
+
+_OBJ = 'OBJ'
+_TEST = 'TEST'
+_LIST_TEST = 'LIST_TEST'
+_LOGICAL = 'LOGICAL'
+_OPTION = 'OPTION'
+
+_VALUE = 'VALUE'
+_IF = 'IF'
+_AND = 'AND'
+_OR = 'OR'
+
+_EQUAL = '=='
+_NOT_EQUAL = '!='
+
+_IGNORE_ERRORS = '+IgnoreErrors'
+_ALL_ENVS = '+AllEnvs'
+
+class Element(object):
+
+    def __init__(self, expression, delimiter):
+        self._delimiter = delimiter
+        self._export_path = None
+        self._parameter_path = None
+        self._parameter_value = None
+        self._export_path, self._parameter_path, self._parameter_value = self._get_vars(expression[0][1], self._export_path, self._parameter_path, self._parameter_value)
+        self._export_path, self._parameter_path, self._parameter_value = self._get_vars(expression[2][1], self._export_path, self._parameter_path, self._parameter_value)
+
+        try:
+            self._export_path.drop_first()
+        except AttributeError:
+            raise ExpressionError('No export')
+
+        self._inv_refs = [ self._export_path ]
+        self._test = expression[1][1]
+
+        if self._parameter_path is not None:
+            self._parameter_path.drop_first()
+            self._refs = [ str(self._parameter_path) ]
+        else:
+            self._refs = []
+
+    def refs(self):
+        return self._refs
+
+    def inv_refs(self):
+        return self._inv_refs
+
+    def value(self, context, items):
+        if self._parameter_path is not None:
+            self._parameter_value = self._resolve(self._parameter_path, context)
+
+        if self._parameter_value is None or self._test is None:
+            raise ExpressionError('Failed to render %s' % str(self), tbFlag=False)
+
+        if self._export_path.exists_in(items):
+            result = False
+            export_value = self._resolve(self._export_path, items)
+            if self._test == _EQUAL:
+                if export_value == self._parameter_value:
+                    result = True
+            elif self._test == _NOT_EQUAL:
+                if export_value != self._parameter_value:
+                    result = True
+            else:
+                raise ExpressionError('Unknown test {0}'.format(self._test), tbFlag=False)
+            return result
+        else:
+            return False
+
+    def _resolve(self, path, dictionary):
+        try:
+            return path.get_value(dictionary)
+        except KeyError as e:
+            raise ResolveError(str(path))
+
+    def _get_vars(self, var, export, parameter, value):
+        if isinstance(var, str):
+            path = DictPath(self._delimiter, var)
+            if path.path[0].lower() == 'exports':
+                export = path
+            elif path.path[0].lower() == 'self':
+                parameter = path
+            elif path.path[0].lower() == 'true':
+                value = True
+            elif path.path[0].lower() == 'false':
+                value = False
+            else:
+                value = var
+        else:
+            value = var
+        return export, parameter, value
+
+
+class Question(object):
+
+    def __init__(self, expression, delimiter):
+        self._elements = []
+        self._operators = []
+        self._delimiter = delimiter
+        self._refs = []
+        self._inv_refs = []
+        i = 0
+        while i < len(expression):
+            e = Element(expression[i:], self._delimiter)
+            self._elements.append(e)
+            self._refs.extend(e.refs())
+            self._inv_refs.extend(e.inv_refs())
+            i += 3
+            if i < len(expression):
+                self._operators.append(expression[i][1])
+                i += 1
+
+    def refs(self):
+        return self._refs
+
+    def inv_refs(self):
+        return self._inv_refs
+
+    def value(self, context, items):
+        if len(self._elements) == 0:
+            return True
+        elif len(self._elements) == 1:
+            return self._elements[0].value(context, items)
+        else:
+            result = self._elements[0].value(context, items)
+            for i in range(0, len(self._elements)-1):
+                next_result = self._elements[i+1].value(context, items)
+                if self._operators[i] == _AND:
+                    result = result and next_result
+                elif self._operators[i] == _OR:
+                    result = result or next_result
+                else:
+                    raise ExpressionError('Unknown operator {0} {1}'.format(self._operators[i], self.elements), tbFlag=False)
+            return result
+
+
+class InvItem(Item):
+
+    def _get_parser():
+
+        def _object(string, location, tokens):
+            token = tokens[0]
+            tokens[0] = (_OBJ, token)
+
+        def _integer(string, location, tokens):
+            try:
+                token = int(tokens[0])
+            except ValueError:
+                token = tokens[0]
+            tokens[0] = (_OBJ, token)
+
+        def _number(string, location, tokens):
+            try:
+                token = float(tokens[0])
+            except ValueError:
+                token = tokens[0]
+            tokens[0] = (_OBJ, token)
+
+        def _option(string, location, tokens):
+            token = tokens[0]
+            tokens[0] = (_OPTION, token)
+
+        def _test(string, location, tokens):
+            token = tokens[0]
+            tokens[0] = (_TEST, token)
+
+        def _logical(string, location, tokens):
+            token = tokens[0]
+            tokens[0] = (_LOGICAL, token)
+
+        def _if(string, location, tokens):
+            token = tokens[0]
+            tokens[0] = (_IF, token)
+
+        def _expr_var(string, location, tokens):
+            token = tokens[0]
+            tokens[0] = (_VALUE, token)
+
+        def _expr_test(string, location, tokens):
+            token = tokens[0]
+            tokens[0] = (_TEST, token)
+
+        def _expr_list_test(string, location, tokens):
+            token = tokens[0]
+            tokens[0] = (_LIST_TEST, token)
+
+        white_space = pp.White().suppress()
+        end = pp.StringEnd()
+        ignore_errors = pp.CaselessLiteral(_IGNORE_ERRORS)
+        all_envs = pp.CaselessLiteral(_ALL_ENVS)
+        option = (ignore_errors | all_envs).setParseAction(_option)
+        options = pp.Group(pp.ZeroOrMore(option + white_space))
+        operator_test = (pp.Literal(_EQUAL) | pp.Literal(_NOT_EQUAL)).setParseAction(_test)
+        operator_logical = (pp.CaselessLiteral(_AND) | pp.CaselessLiteral(_OR)).setParseAction(_logical)
+        begin_if = pp.CaselessLiteral(_IF, ).setParseAction(_if)
+        obj = pp.Word(pp.printables).setParseAction(_object)
+        integer = pp.Word('0123456789-').setParseAction(_integer)
+        number = pp.Word('0123456789-.').setParseAction(_number)
+        item = integer | number | obj
+        single_test = white_space + item + white_space + operator_test + white_space + item
+        additional_test = white_space + operator_logical + single_test
+        expr_var = pp.Group(obj + pp.Optional(white_space) + end).setParseAction(_expr_var)
+        expr_test = pp.Group(obj + white_space + begin_if + single_test + pp.ZeroOrMore(additional_test) + end).setParseAction(_expr_test)
+        expr_list_test = pp.Group(begin_if + single_test + pp.ZeroOrMore(additional_test) + end).setParseAction(_expr_list_test)
+        expr = (expr_test | expr_var | expr_list_test)
+        line = options + expr + end
+        return line
+
+    _parser = _get_parser()
+
+    def __init__(self, item, settings):
+        self.type = Item.INV_QUERY
+        self._settings = settings
+        self._needs_all_envs = False
+        self._ignore_failed_render = self._settings.inventory_ignore_failed_render
+        self._expr_text = item.render(None, None)
+        self._parse_expression(self._expr_text)
+
+    def _parse_expression(self, expr):
+        try:
+            tokens = InvItem._parser.parseString(expr).asList()
+        except pp.ParseException as e:
+            raise ParseError(e.msg, e.line, e.col, e.lineno)
+
+        if len(tokens) == 1:
+            self._expr_type = tokens[0][0]
+            self._expr = list(tokens[0][1])
+        elif len(tokens) == 2:
+            for opt in tokens[0]:
+                if opt[1] == _IGNORE_ERRORS:
+                    self._ignore_failed_render = True
+                elif opt[1] == _ALL_ENVS:
+                    self._needs_all_envs = True
+            self._expr_type = tokens[1][0]
+            self._expr = list(tokens[1][1])
+        else:
+            raise ExpressionError('Failed to parse %s' % str(tokens), tbFlag=False)
+
+        if self._expr_type == _VALUE:
+            self._value_path = DictPath(self._settings.delimiter, self._expr[0][1]).drop_first()
+            self._question = Question([], self._settings.delimiter)
+            self._refs = []
+            self._inv_refs = [ self._value_path ]
+        elif self._expr_type == _TEST:
+            self._value_path = DictPath(self._settings.delimiter, self._expr[0][1]).drop_first()
+            self._question = Question(self._expr[2:], self._settings.delimiter)
+            self._refs = self._question.refs()
+            self._inv_refs = self._question.inv_refs()
+            self._inv_refs.append(self._value_path)
+        elif self._expr_type == _LIST_TEST:
+            self._value_path = None
+            self._question = Question(self._expr[1:], self._settings.delimiter)
+            self._refs = self._question.refs()
+            self._inv_refs = self._question.inv_refs()
+        else:
+            raise ExpressionError('Unknown expression type: %s' % self._expr_type, tbFlag=False)
+
+    def assembleRefs(self, context):
+        return
+
+    def contents(self):
+        return self._expr_text
+
+    def has_inv_query(self):
+        return True
+
+    def has_references(self):
+        return len(self._question.refs()) > 0
+
+    def get_references(self):
+        return self._question.refs()
+
+    def get_inv_references(self):
+        return self._inv_refs
+
+    def needs_all_envs(self):
+        return self._needs_all_envs
+
+    def ignore_failed_render(self):
+        return self._ignore_failed_render
+
+    def _resolve(self, path, dictionary):
+        try:
+            return path.get_value(dictionary)
+        except KeyError as e:
+            raise ResolveError(str(path))
+
+    def _value_expression(self, inventory):
+        results = {}
+        for (node, items) in iteritems(inventory):
+            if self._value_path.exists_in(items):
+                results[node] = copy.deepcopy(self._resolve(self._value_path, items))
+        return results
+
+    def _test_expression(self, context, inventory):
+        if self._value_path is None:
+            ExpressionError('Failed to render %s' % str(self), tbFlag=False)
+
+        results = {}
+        for (node, items) in iteritems(inventory):
+            if self._question.value(context, items) and self._value_path.exists_in(items):
+                results[node] = copy.deepcopy(self._resolve(self._value_path, items))
+        return results
+
+    def _list_test_expression(self, context, inventory):
+        results = []
+        for (node, items) in iteritems(inventory):
+            if self._question.value(context, items):
+                results.append(node)
+        return results
+
+    def render(self, context, inventory):
+        if self._expr_type == _VALUE:
+            return self._value_expression(inventory)
+        elif self._expr_type == _TEST:
+            return self._test_expression(context, inventory)
+        elif self._expr_type == _LIST_TEST:
+            return self._list_test_expression(context, inventory)
+        raise ExpressionError('Failed to render %s' % str(self), tbFlag=False)
+
+    def __str__(self):
+        return ' '.join(str(j) for i,j in self._expr)
+
+    def __repr__(self):
+        return 'InvItem(%r)' % self._expr
diff --git a/reclass/values/item.py b/reclass/values/item.py
new file mode 100644
index 0000000..57fd0e3
--- /dev/null
+++ b/reclass/values/item.py
@@ -0,0 +1,43 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+from reclass.utils.dictpath import DictPath
+
+class Item(object):
+
+    COMPOSITE = 1
+    DICTIONARY = 2
+    INV_QUERY = 3
+    LIST = 4
+    REFERENCE = 5
+    SCALAR = 6
+
+    def allRefs(self):
+        return True
+
+    def has_references(self):
+        return False
+
+    def has_inv_query(self):
+        return False
+
+    def is_container(self):
+        return False
+
+    def is_complex(self):
+        return (self.has_references() | self.has_inv_query())
+
+    def contents(self):
+        msg = "Item class {0} does not implement contents()"
+        raise NotImplementedError(msg.format(self.__class__.__name__))
+
+    def merge_over(self, item):
+        msg = "Item class {0} does not implement merge_over()"
+        raise NotImplementedError(msg.format(self.__class__.__name__))
+
+    def render(self, context, exports):
+        msg = "Item class {0} does not implement render()"
+        raise NotImplementedError(msg.format(self.__class__.__name__))
diff --git a/reclass/values/listitem.py b/reclass/values/listitem.py
new file mode 100644
index 0000000..1829e32
--- /dev/null
+++ b/reclass/values/listitem.py
@@ -0,0 +1,41 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+from .item import Item
+from reclass.settings import Settings
+
+class ListItem(Item):
+
+    def __init__(self, item, settings):
+        self.type = Item.LIST
+        self._list = item
+        self._settings = settings
+
+    def contents(self):
+        return self._list
+
+    def is_container(self):
+        return True
+
+    def render(self, context, inventory):
+        return self._list
+
+    def merge_over(self, item):
+        if item.type == Item.LIST:
+            item._list.extend(self._list)
+            return item
+        elif item.type == Item.SCALAR:
+            if item.contents() is None:
+                return self
+            elif self._settings.allow_list_over_scalar:
+                self._list.insert(0, item.contents())
+                return self
+            else:
+                raise TypeError('allow list over scalar = False: cannot merge %s onto %s' % (repr(self), repr(item)))
+        raise TypeError('Cannot merge %s over %s' % (repr(self), repr(item)))
+
+    def __repr__(self):
+        return 'ListItem(%r)' % (self._list)
diff --git a/reclass/values/parser.py b/reclass/values/parser.py
new file mode 100644
index 0000000..a8adcf0
--- /dev/null
+++ b/reclass/values/parser.py
@@ -0,0 +1,64 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+import pyparsing as pp
+
+from .compitem import CompItem
+from .invitem import InvItem
+from .refitem import RefItem
+from .scaitem import ScaItem
+
+from reclass.errors import ParseError
+from reclass.values.parser_funcs import STR, REF, INV
+
+class Parser(object):
+
+    def parse(self, value, settings):
+        self._settings = settings
+        dollars = value.count('$')
+        if dollars == 0:
+            # speed up: only use pyparsing if there is a $ in the string
+            return ScaItem(value, self._settings)
+        elif dollars == 1:
+            # speed up: try a simple reference
+            try:
+                tokens = self._settings.simple_ref_parser.leaveWhitespace().parseString(value).asList()
+            except pp.ParseException:
+                # fall back on the full parser
+                try:
+                    tokens = self._settings.ref_parser.leaveWhitespace().parseString(value).asList()
+                except pp.ParseException as e:
+                    raise ParseError(e.msg, e.line, e.col, e.lineno)
+        else:
+            # use the full parser
+            try:
+                tokens = self._settings.ref_parser.leaveWhitespace().parseString(value).asList()
+            except pp.ParseException as e:
+                raise ParseError(e.msg, e.line, e.col, e.lineno)
+
+        items = self._create_items(tokens)
+        if len(items) == 1:
+            return items[0]
+        else:
+            return CompItem(items, self._settings)
+
+    _create_dict = { STR: (lambda s, v: ScaItem(v, s._settings)),
+                     REF: (lambda s, v: s._create_ref(v)),
+                     INV: (lambda s, v: s._create_inv(v)) }
+
+    def _create_items(self, tokens):
+        return [ self._create_dict[t](self, v) for t, v in tokens ]
+
+    def _create_ref(self, tokens):
+        items = [ self._create_dict[t](self, v) for t, v in tokens ]
+        return RefItem(items, self._settings)
+
+    def _create_inv(self, tokens):
+        items = [ ScaItem(v, self._settings) for t, v in tokens ]
+        if len(items) == 1:
+            return InvItem(items[0], self._settings)
+        else:
+            return InvItem(CompItem(items), self._settings)
diff --git a/reclass/values/parser_funcs.py b/reclass/values/parser_funcs.py
new file mode 100644
index 0000000..bd5a1ba
--- /dev/null
+++ b/reclass/values/parser_funcs.py
@@ -0,0 +1,99 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+import pyparsing as pp
+
+STR = 1
+REF = 2
+INV = 3
+
+def _string(string, location, tokens):
+    token = tokens[0]
+    tokens[0] = (STR, token)
+
+def _reference(string, location, tokens):
+    token = list(tokens[0])
+    tokens[0] = (REF, token)
+
+def _invquery(string, location, tokens):
+    token = list(tokens[0])
+    tokens[0] = (INV, token)
+
+def get_ref_parser(escape_character, reference_sentinels, export_sentinels):
+    _ESCAPE = escape_character
+    _DOUBLE_ESCAPE = _ESCAPE + _ESCAPE
+
+    _REF_OPEN = reference_sentinels[0]
+    _REF_CLOSE = reference_sentinels[1]
+    _REF_CLOSE_FIRST = _REF_CLOSE[0]
+    _REF_ESCAPE_OPEN = _ESCAPE + _REF_OPEN
+    _REF_ESCAPE_CLOSE = _ESCAPE + _REF_CLOSE
+    _REF_DOUBLE_ESCAPE_OPEN = _DOUBLE_ESCAPE + _REF_OPEN
+    _REF_DOUBLE_ESCAPE_CLOSE = _DOUBLE_ESCAPE + _REF_CLOSE
+    _REF_EXCLUDES = _ESCAPE + _REF_OPEN + _REF_CLOSE
+
+    _INV_OPEN = export_sentinels[0]
+    _INV_CLOSE = export_sentinels[1]
+    _INV_CLOSE_FIRST = _INV_CLOSE[0]
+    _INV_ESCAPE_OPEN = _ESCAPE + _INV_OPEN
+    _INV_ESCAPE_CLOSE = _ESCAPE + _INV_CLOSE
+    _INV_DOUBLE_ESCAPE_OPEN = _DOUBLE_ESCAPE + _INV_OPEN
+    _INV_DOUBLE_ESCAPE_CLOSE = _DOUBLE_ESCAPE + _INV_CLOSE
+    _INV_EXCLUDES = _ESCAPE + _INV_OPEN + _INV_CLOSE
+
+    _EXCLUDES = _ESCAPE + _REF_OPEN + _REF_CLOSE + _INV_OPEN + _INV_CLOSE
+
+    double_escape = pp.Combine(pp.Literal(_DOUBLE_ESCAPE) + pp.MatchFirst([pp.FollowedBy(_REF_OPEN), pp.FollowedBy(_REF_CLOSE),
+                               pp.FollowedBy(_INV_OPEN), pp.FollowedBy(_INV_CLOSE)])).setParseAction(pp.replaceWith(_ESCAPE))
+
+    ref_open = pp.Literal(_REF_OPEN).suppress()
+    ref_close = pp.Literal(_REF_CLOSE).suppress()
+    ref_not_open = ~pp.Literal(_REF_OPEN) + ~pp.Literal(_REF_ESCAPE_OPEN) + ~pp.Literal(_REF_DOUBLE_ESCAPE_OPEN)
+    ref_not_close = ~pp.Literal(_REF_CLOSE) + ~pp.Literal(_REF_ESCAPE_CLOSE) + ~pp.Literal(_REF_DOUBLE_ESCAPE_CLOSE)
+    ref_escape_open = pp.Literal(_REF_ESCAPE_OPEN).setParseAction(pp.replaceWith(_REF_OPEN))
+    ref_escape_close = pp.Literal(_REF_ESCAPE_CLOSE).setParseAction(pp.replaceWith(_REF_CLOSE))
+    ref_text = pp.CharsNotIn(_REF_EXCLUDES) | pp.CharsNotIn(_REF_CLOSE_FIRST, exact=1)
+    ref_content = pp.Combine(pp.OneOrMore(ref_not_open + ref_not_close + ref_text))
+    ref_string = pp.MatchFirst([double_escape, ref_escape_open, ref_escape_close, ref_content]).setParseAction(_string)
+    ref_item = pp.Forward()
+    ref_items = pp.OneOrMore(ref_item)
+    reference = (ref_open + pp.Group(ref_items) + ref_close).setParseAction(_reference)
+    ref_item << (reference | ref_string)
+
+    inv_open = pp.Literal(_INV_OPEN).suppress()
+    inv_close = pp.Literal(_INV_CLOSE).suppress()
+    inv_not_open = ~pp.Literal(_INV_OPEN) + ~pp.Literal(_INV_ESCAPE_OPEN) + ~pp.Literal(_INV_DOUBLE_ESCAPE_OPEN)
+    inv_not_close = ~pp.Literal(_INV_CLOSE) + ~pp.Literal(_INV_ESCAPE_CLOSE) + ~pp.Literal(_INV_DOUBLE_ESCAPE_CLOSE)
+    inv_escape_open = pp.Literal(_INV_ESCAPE_OPEN).setParseAction(pp.replaceWith(_INV_OPEN))
+    inv_escape_close = pp.Literal(_INV_ESCAPE_CLOSE).setParseAction(pp.replaceWith(_INV_CLOSE))
+    inv_text = pp.CharsNotIn(_INV_CLOSE_FIRST)
+    inv_content = pp.Combine(pp.OneOrMore(inv_not_close + inv_text))
+    inv_string = pp.MatchFirst([double_escape, inv_escape_open, inv_escape_close, inv_content]).setParseAction(_string)
+    inv_items = pp.OneOrMore(inv_string)
+    export = (inv_open + pp.Group(inv_items) + inv_close).setParseAction(_invquery)
+
+    text = pp.CharsNotIn(_EXCLUDES) | pp.CharsNotIn('', exact=1)
+    content = pp.Combine(pp.OneOrMore(ref_not_open + inv_not_open + text))
+    string = pp.MatchFirst([double_escape, ref_escape_open, inv_escape_open, content]).setParseAction(_string)
+
+    item = reference | export | string
+    line = pp.OneOrMore(item) + pp.StringEnd()
+    return line
+
+def get_simple_ref_parser(escape_character, reference_sentinels, export_sentinels):
+    _ESCAPE = escape_character
+    _REF_OPEN = reference_sentinels[0]
+    _REF_CLOSE = reference_sentinels[1]
+    _INV_OPEN = export_sentinels[0]
+    _INV_CLOSE = export_sentinels[1]
+    _EXCLUDES = _ESCAPE + _REF_OPEN + _REF_CLOSE + _INV_OPEN + _INV_CLOSE
+
+    string = pp.CharsNotIn(_EXCLUDES).setParseAction(_string)
+    ref_open = pp.Literal(_REF_OPEN).suppress()
+    ref_close = pp.Literal(_REF_CLOSE).suppress()
+    reference = (ref_open + pp.Group(string) + ref_close).setParseAction(_reference)
+    line = pp.StringStart() + pp.Optional(string) + reference + pp.Optional(string) + pp.StringEnd()
+    return line
diff --git a/reclass/values/refitem.py b/reclass/values/refitem.py
new file mode 100644
index 0000000..3e3341c
--- /dev/null
+++ b/reclass/values/refitem.py
@@ -0,0 +1,70 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+from .item import Item
+from reclass.defaults import REFERENCE_SENTINELS
+from reclass.settings import Settings
+from reclass.utils.dictpath import DictPath
+from reclass.errors import ResolveError
+
+
+class RefItem(Item):
+
+    def __init__(self, items, settings):
+        self.type = Item.REFERENCE
+        self._settings = settings
+        self._items = items
+        self._refs = []
+        self._allRefs = False
+        self.assembleRefs()
+
+    def assembleRefs(self, context={}):
+        self._refs = []
+        self._allRefs = True
+        for item in self._items:
+            if item.has_references():
+                item.assembleRefs(context)
+                self._refs.extend(item.get_references())
+                if item.allRefs() == False:
+                    self._allRefs = False
+        try:
+            strings = [ str(i.render(context, None)) for i in self._items ]
+            value = "".join(strings)
+            self._refs.append(value)
+        except ResolveError as e:
+            self._allRefs = False
+
+    def contents(self):
+        return self._items
+
+    def allRefs(self):
+        return self._allRefs
+
+    def has_references(self):
+        return len(self._refs) > 0
+
+    def get_references(self):
+        return self._refs
+
+    def _resolve(self, ref, context):
+        path = DictPath(self._settings.delimiter, ref)
+        try:
+            return path.get_value(context)
+        except (KeyError, TypeError) as e:
+            raise ResolveError(ref)
+
+    def render(self, context, inventory):
+        if len(self._items) == 1:
+            return self._resolve(self._items[0].render(context, inventory), context)
+        strings = [ str(i.render(context, inventory)) for i in self._items ]
+        return self._resolve("".join(strings), context)
+
+    def __repr__(self):
+        return 'RefItem(%r)' % self._items
+
+    def __str__(self):
+        strings = [ str(i) for i in self._items ]
+        return '{0}{1}{2}'.format(REFERENCE_SENTINELS[0], ''.join(strings), REFERENCE_SENTINELS[1])
diff --git a/reclass/values/scaitem.py b/reclass/values/scaitem.py
new file mode 100644
index 0000000..f4265b5
--- /dev/null
+++ b/reclass/values/scaitem.py
@@ -0,0 +1,42 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+from reclass.settings import Settings
+from .item import Item
+
+class ScaItem(Item):
+
+    def __init__(self, value, settings):
+        self.type = Item.SCALAR
+        self._value = value
+        self._settings = settings
+
+    def contents(self):
+        return self._value
+
+    def merge_over(self, item):
+        if item.type == Item.SCALAR or item.type == Item.COMPOSITE:
+            return self
+        elif item.type == Item.LIST:
+            if self._settings.allow_scalar_over_list or (self._settings.allow_none_override and self._value is None):
+                return self
+            else:
+                raise TypeError('allow scalar over list = False: cannot merge %s over %s' % (repr(self), repr(item)))
+        elif item.type == Item.DICTIONARY:
+            if self._settings.allow_scalar_over_dict or (self._settings.allow_none_override and self._value is None):
+                return self
+            else:
+                raise TypeError('allow scalar over dict = False: cannot merge %s over %s' % (repr(self), repr(item)))
+        raise TypeError('Cannot merge %s over %s' % (repr(self), repr(item)))
+
+    def render(self, context, inventory):
+        return self._value
+
+    def __repr__(self):
+        return 'ScaItem({0!r})'.format(self._value)
+
+    def __str__(self):
+        return str(self._value)
diff --git a/reclass/values/tests/__init__.py b/reclass/values/tests/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/reclass/values/tests/__init__.py
diff --git a/reclass/utils/tests/test_refvalue.py b/reclass/values/tests/test_value.py
similarity index 65%
rename from reclass/utils/tests/test_refvalue.py
rename to reclass/values/tests/test_value.py
index 23d7e7b..84403d3 100644
--- a/reclass/utils/tests/test_refvalue.py
+++ b/reclass/values/tests/test_value.py
@@ -7,16 +7,18 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 
-from reclass.utils.refvalue import RefValue
-from reclass.defaults import PARAMETER_INTERPOLATION_SENTINELS, \
-        PARAMETER_INTERPOLATION_DELIMITER
-from reclass.errors import UndefinedVariableError, \
-        IncompleteInterpolationError
+import pyparsing as pp
+
+from reclass.settings import Settings
+from reclass.values.value import Value
+from reclass.errors import ResolveError, ParseError
 import unittest
 
+SETTINGS = Settings()
+
 def _var(s):
-    return '%s%s%s' % (PARAMETER_INTERPOLATION_SENTINELS[0], s,
-                       PARAMETER_INTERPOLATION_SENTINELS[1])
+    return '%s%s%s' % (SETTINGS.reference_sentinels[0], s,
+                       SETTINGS.reference_sentinels[1])
 
 CONTEXT = {'favcolour':'yellow',
            'motd':{'greeting':'Servus!',
@@ -31,18 +33,18 @@
 def _poor_mans_template(s, var, value):
     return s.replace(_var(var), value)
 
-class TestRefValue(unittest.TestCase):
+class TestValue(unittest.TestCase):
 
     def test_simple_string(self):
         s = 'my cat likes to hide in boxes'
-        tv = RefValue(s)
+        tv = Value(s, SETTINGS, '')
         self.assertFalse(tv.has_references())
-        self.assertEquals(tv.render(CONTEXT), s)
+        self.assertEquals(tv.render(CONTEXT, None), s)
 
     def _test_solo_ref(self, key):
         s = _var(key)
-        tv = RefValue(s)
-        res = tv.render(CONTEXT)
+        tv = Value(s, SETTINGS, '')
+        res = tv.render(CONTEXT, None)
         self.assertTrue(tv.has_references())
         self.assertEqual(res, CONTEXT[key])
 
@@ -63,65 +65,65 @@
 
     def test_single_subst_bothends(self):
         s = 'I like ' + _var('favcolour') + ' and I like it'
-        tv = RefValue(s)
+        tv = Value(s, SETTINGS, '')
         self.assertTrue(tv.has_references())
-        self.assertEqual(tv.render(CONTEXT),
+        self.assertEqual(tv.render(CONTEXT, None),
                          _poor_mans_template(s, 'favcolour',
                                              CONTEXT['favcolour']))
 
     def test_single_subst_start(self):
         s = _var('favcolour') + ' is my favourite colour'
-        tv = RefValue(s)
+        tv = Value(s, SETTINGS, '')
         self.assertTrue(tv.has_references())
-        self.assertEqual(tv.render(CONTEXT),
+        self.assertEqual(tv.render(CONTEXT, None),
                          _poor_mans_template(s, 'favcolour',
                                              CONTEXT['favcolour']))
 
     def test_single_subst_end(self):
         s = 'I like ' + _var('favcolour')
-        tv = RefValue(s)
+        tv = Value(s, SETTINGS, '')
         self.assertTrue(tv.has_references())
-        self.assertEqual(tv.render(CONTEXT),
+        self.assertEqual(tv.render(CONTEXT, None),
                          _poor_mans_template(s, 'favcolour',
                                              CONTEXT['favcolour']))
 
     def test_deep_subst_solo(self):
-        var = PARAMETER_INTERPOLATION_DELIMITER.join(('motd', 'greeting'))
-        s = _var(var)
-        tv = RefValue(s)
+        motd = SETTINGS.delimiter.join(('motd', 'greeting'))
+        s = _var(motd)
+        tv = Value(s, SETTINGS, '')
         self.assertTrue(tv.has_references())
-        self.assertEqual(tv.render(CONTEXT),
-                         _poor_mans_template(s, var,
+        self.assertEqual(tv.render(CONTEXT, None),
+                         _poor_mans_template(s, motd,
                                              CONTEXT['motd']['greeting']))
 
     def test_multiple_subst(self):
-        greet = PARAMETER_INTERPOLATION_DELIMITER.join(('motd', 'greeting'))
+        greet = SETTINGS.delimiter.join(('motd', 'greeting'))
         s = _var(greet) + ' I like ' + _var('favcolour') + '!'
-        tv = RefValue(s)
+        tv = Value(s, SETTINGS, '')
         self.assertTrue(tv.has_references())
         want = _poor_mans_template(s, greet, CONTEXT['motd']['greeting'])
         want = _poor_mans_template(want, 'favcolour', CONTEXT['favcolour'])
-        self.assertEqual(tv.render(CONTEXT), want)
+        self.assertEqual(tv.render(CONTEXT, None), want)
 
     def test_multiple_subst_flush(self):
-        greet = PARAMETER_INTERPOLATION_DELIMITER.join(('motd', 'greeting'))
+        greet = SETTINGS.delimiter.join(('motd', 'greeting'))
         s = _var(greet) + ' I like ' + _var('favcolour')
-        tv = RefValue(s)
+        tv = Value(s, SETTINGS, '')
         self.assertTrue(tv.has_references())
         want = _poor_mans_template(s, greet, CONTEXT['motd']['greeting'])
         want = _poor_mans_template(want, 'favcolour', CONTEXT['favcolour'])
-        self.assertEqual(tv.render(CONTEXT), want)
+        self.assertEqual(tv.render(CONTEXT, None), want)
 
     def test_undefined_variable(self):
         s = _var('no_such_variable')
-        tv = RefValue(s)
-        with self.assertRaises(UndefinedVariableError):
-            tv.render(CONTEXT)
+        tv = Value(s, SETTINGS, '')
+        with self.assertRaises(ResolveError):
+            tv.render(CONTEXT, None)
 
     def test_incomplete_variable(self):
-        s = PARAMETER_INTERPOLATION_SENTINELS[0] + 'incomplete'
-        with self.assertRaises(IncompleteInterpolationError):
-            tv = RefValue(s)
+        s = SETTINGS.reference_sentinels[0] + 'incomplete'
+        with self.assertRaises(ParseError):
+            tv = Value(s, SETTINGS, '')
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/reclass/values/value.py b/reclass/values/value.py
new file mode 100644
index 0000000..1a5b450
--- /dev/null
+++ b/reclass/values/value.py
@@ -0,0 +1,100 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+from .parser import Parser
+from .dictitem import DictItem
+from .listitem import ListItem
+from .scaitem import ScaItem
+from reclass.errors import InterpolationError
+
+class Value(object):
+
+    _parser = Parser()
+
+    def __init__(self, value, settings, uri, parse_string=True):
+        self._settings = settings
+        self._uri = uri
+        self._overwrite = False
+        if isinstance(value, str):
+            if parse_string:
+                try:
+                    self._item = self._parser.parse(value, self._settings)
+                except InterpolationError as e:
+                    e.uri = self._uri
+                    raise
+            else:
+                self._item = ScaItem(value, self._settings)
+        elif isinstance(value, list):
+            self._item = ListItem(value, self._settings)
+        elif isinstance(value, dict):
+            self._item = DictItem(value, self._settings)
+        else:
+            self._item = ScaItem(value, self._settings)
+
+    @property
+    def overwrite(self):
+        return self._overwrite
+
+    @overwrite.setter
+    def overwrite(self, overwrite):
+        self._overwrite = overwrite
+
+    def uri(self):
+        return self._uri
+
+    def is_container(self):
+        return self._item.is_container()
+
+    def allRefs(self):
+        return self._item.allRefs()
+
+    def has_references(self):
+        return self._item.has_references()
+
+    def has_inv_query(self):
+        return self._item.has_inv_query()
+
+    def needs_all_envs(self):
+        if self._item.has_inv_query():
+            return self._item.needs_all_envs()
+        else:
+            return False
+
+    def ignore_failed_render(self):
+        return self._item.ignore_failed_render()
+
+    def is_complex(self):
+        return self._item.is_complex()
+
+    def get_references(self):
+        return self._item.get_references()
+
+    def get_inv_references(self):
+        return self._item.get_inv_references()
+
+    def assembleRefs(self, context):
+        if self._item.has_references():
+            self._item.assembleRefs(context)
+
+    def render(self, context, inventory):
+        try:
+            return self._item.render(context, inventory)
+        except InterpolationError as e:
+            e.uri = self._uri
+            raise
+
+    def contents(self):
+        return self._item.contents()
+
+    def merge_over(self, value):
+        self._item = self._item.merge_over(value._item)
+        return self
+
+    def __repr__(self):
+        return 'Value(%r)' % self._item
+
+    def __str__(self):
+        return str(self._item)
diff --git a/reclass/values/valuelist.py b/reclass/values/valuelist.py
new file mode 100644
index 0000000..bdfa01a
--- /dev/null
+++ b/reclass/values/valuelist.py
@@ -0,0 +1,135 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass
+#
+
+from __future__ import print_function
+
+import copy
+import sys
+
+from reclass.errors import ResolveError
+
+class ValueList(object):
+
+    def __init__(self, value, settings):
+        self._settings = settings
+        self._refs = []
+        self._allRefs = True
+        self._values = [ value ]
+        self._inv_refs = []
+        self._has_inv_query = False
+        self._ignore_failed_render = False
+        self._update()
+
+    def append(self, value):
+        self._values.append(value)
+        self._update()
+
+    def extend(self, values):
+        self._values.extend(values._values)
+        self._update()
+
+    def _update(self):
+        self.assembleRefs()
+        self._check_for_inv_query()
+
+    def has_references(self):
+        return len(self._refs) > 0
+
+    def has_inv_query(self):
+        return self._has_inv_query
+
+    def get_inv_references(self):
+        return self._inv_refs
+
+    def is_complex(self):
+        return (self.has_references() | self.has_inv_query())
+
+    def get_references(self):
+        return self._refs
+
+    def allRefs(self):
+        return self._allRefs
+
+    def ignore_failed_render(self):
+        return self._ignore_failed_render
+
+    def _check_for_inv_query(self):
+        self._has_inv_query = False
+        self._ignore_failed_render = True
+        for value in self._values:
+            if value.has_inv_query():
+                self._inv_refs.extend(value.get_inv_references)
+                self._has_inv_query = True
+                if vale.ignore_failed_render() is False:
+                    self._ignore_failed_render = False
+        if self._has_inv_query is False:
+            self._ignore_failed_render = False
+
+    def assembleRefs(self, context={}):
+        self._refs = []
+        self._allRefs = True
+        for value in self._values:
+            value.assembleRefs(context)
+            if value.has_references():
+                self._refs.extend(value.get_references())
+            if value.allRefs() is False:
+                self._allRefs = False
+
+    def merge(self):
+        output = None
+        for n, value in enumerate(self._values):
+            if output is None:
+                output = value
+            else:
+                output = value.merge_over(output)
+        return output
+
+    def render(self, context, inventory):
+        from reclass.datatypes.parameters import Parameters
+
+        output = None
+        deepCopied = False
+        last_error = None
+        for n, value in enumerate(self._values):
+            try:
+                new = value.render(context, inventory)
+            except ResolveError as e:
+                if self._settings.ignore_overwritten_missing_references and not isinstance(output, (dict, list)) and n != (len(self._values)-1):
+                    new = None
+                    last_error = e
+                    print("[WARNING] Reference '%s' undefined" % str(value), file=sys.stderr)
+                else:
+                    raise e
+
+            if output is None or value.overwrite:
+                output = new
+                deepCopied = False
+            else:
+                if isinstance(output, dict) and isinstance(new, dict):
+                    p1 = Parameters(output, self._settings, None, parse_strings=False)
+                    p2 = Parameters(new, self._settings, None, parse_strings=False)
+                    p1.merge(p2)
+                    output = p1.as_dict()
+                    continue
+                elif isinstance(output, list) and isinstance(new, list):
+                    if not deepCopied:
+                        output = copy.deepcopy(output)
+                        deepCopied = True
+                    output.extend(new)
+                    continue
+                elif isinstance(output, (dict, list)) or isinstance(new, (dict, list)):
+                    raise TypeError('Cannot merge %s over %s' % (repr(self._values[n]), repr(self._values[n-1])))
+                else:
+                    output = new
+                    deepCopied = False
+
+        if isinstance(output, (dict, list)) and last_error is not None:
+            raise last_error
+
+        return output
+
+    def __repr__(self):
+        return 'ValueList(%r)' % self._values
diff --git a/reclass/version.py b/reclass/version.py
index 64923eb..664fd6f 100644
--- a/reclass/version.py
+++ b/reclass/version.py
@@ -7,10 +7,12 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 RECLASS_NAME = 'reclass'
-DESCRIPTION = 'merge data by recursive descent down an ancestry hierarchy'
-VERSION = '1.4.1'
-AUTHOR = 'martin f. krafft'
-AUTHOR_EMAIL = 'reclass@pobox.madduck.net'
-COPYRIGHT = 'Copyright © 2007–14 ' + AUTHOR
+DESCRIPTION = 'merge data by recursive descent down an ancestry hierarchy (forked extended version)'
+VERSION = '1.5.3'
+AUTHOR = 'martin f. krafft / Andrew Pickford / salt-formulas community'
+AUTHOR_EMAIL = 'salt-formulas@freelists.org'
+MAINTAINER = 'salt-formulas community'
+MAINTAINER_EMAIL = 'salt-formulas@freelists.org'
+COPYRIGHT = 'Copyright © 2007–14 martin f. krafft, extensions © 2017 Andrew Pickford, extensions © salt-formulas community'
 LICENCE = 'Artistic Licence 2.0'
-URL = 'https://github.com/madduck/reclass'
+URL = 'https://github.com/salt-formulas/reclass'
diff --git a/releasenotes/config.yaml b/releasenotes/config.yaml
new file mode 100644
index 0000000..6a6923d
--- /dev/null
+++ b/releasenotes/config.yaml
@@ -0,0 +1,66 @@
+---
+# Usage:
+#
+# reno -qd .releasenotes list
+# reno -qd .releasenotes new slug-title --edit
+# reno -qd .releasenotes report --no-show-source
+
+# Change prelude_section_name to 'summary' from default value prelude
+prelude_section_name: summary
+show_source: False
+sections:
+  - [summary, Summary]
+  - [features, New features]
+  - [fixes, Bug fixes]
+  - [others, Other notes]
+template: |
+  ---
+  # Author the following sections or remove the section if it is not related.
+  # Use one release note per a feature.
+  #
+  # If you miss a section from the list below, please first submit a review
+  # adding it to .releasenotes/config.yaml.
+  #
+  # Format content with reStructuredText (RST).
+  # **Formatting examples:**
+  # - |
+  #   This is a brief description of the feature. It may include a
+  #   number of components:
+  #
+  #   * List item 1
+  #   * List item 2.
+  #     This code block below will appear as part of the list item 2:
+  #
+  #     .. code-block:: yaml
+  #
+  #        classes:
+  #        - system.class.to.load
+  #
+  #   The code block below will appear on the same level as the feature
+  #   description:
+  #
+  #   .. code-block:: text
+  #
+  #      provide model/formula pillar snippets
+
+
+  summary: >
+    This section is not mandatory. Use it to highlight the change.
+
+  features:
+    - Use the list to record summary of **NEW** features
+    - Provide detailed description of the feature indicating the use cases
+      when users benefit from using it
+    - Provide steps to deploy the feature (if the procedure is complicated
+      indicate during what stage of the deployment workflow it should be
+      deployed).
+    - Provide troubleshooting information, if any.
+
+  fixes:
+    - Use the list to record summary of a bug fix for blocker, critical.
+    - Provide a brief summary of what has been fixed.
+
+  others:
+    - Author any additional notes. Use this section if note is not related to
+      any of the common sections above.
+
diff --git a/releasenotes/notes/escaping-references-e76699d8ca010013.yaml b/releasenotes/notes/escaping-references-e76699d8ca010013.yaml
new file mode 100644
index 0000000..41845ee
--- /dev/null
+++ b/releasenotes/notes/escaping-references-e76699d8ca010013.yaml
@@ -0,0 +1,3 @@
+---
+others:
+  - The escaping of references changes how the constructs '\${xxx}' and '\\${xxx}' are rendered.
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..66f0f4b
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1,4 @@
+pyparsing
+pyyaml
+pygit2
+six
diff --git a/setup.cfg b/setup.cfg
new file mode 100644
index 0000000..c5cfe6b
--- /dev/null
+++ b/setup.cfg
@@ -0,0 +1,6 @@
+[bdist_wheel]
+# This flag says that the code is written to work on both Python 2 and Python
+# 3. If at all possible, it is good practice to do this. If you cannot, you
+# will need to generate wheels for each Python version that you support.
+universal=0
+
diff --git a/setup.py b/setup.py
index c0fd5d8..5b4b8b6 100644
--- a/setup.py
+++ b/setup.py
@@ -10,6 +10,16 @@
 from reclass.version import *
 from setuptools import setup, find_packages
 
+# use consistent encoding of readme for pypi
+from codecs import open
+from os import path
+
+here = path.abspath(path.dirname(__file__))
+
+# Get the long description from the README file
+with open(path.join(here, 'README.rst'), encoding='utf-8') as f:
+    long_description = f.read()
+
 ADAPTERS = ['salt', 'ansible']
 console_scripts = ['reclass = reclass.cli:main']
 console_scripts.extend('reclass-{0} = reclass.adapters.{0}:cli'.format(i)
@@ -18,12 +28,25 @@
 setup(
     name = RECLASS_NAME,
     description = DESCRIPTION,
+    long_description=long_description,
     version = VERSION,
     author = AUTHOR,
     author_email = AUTHOR_EMAIL,
+    maintainer = MAINTAINER,
+    maintainer_email = MAINTAINER_EMAIL,
     license = LICENCE,
     url = URL,
-    packages = find_packages(),
+    packages = find_packages(exclude=['*tests']), #FIXME validate this
     entry_points = { 'console_scripts': console_scripts },
-    install_requires = ['pyyaml']
+    install_requires = ['pyparsing', 'pyyaml', 'six'], #FIXME pygit2 (require libffi-dev, libgit2-dev 0.26.x )
+
+    classifiers=[
+        'Development Status :: 4 - Beta',
+        'Intended Audience :: System Administrators',
+        'Topic :: System :: Systems Administration',
+        'License :: OSI Approved :: Artistic License',
+        'Programming Language :: Python :: 2.7',
+    ],
+
+    keywords='enc ansible salt'
 )
diff --git a/test/model/default/classes/first.yml b/test/model/default/classes/first.yml
new file mode 100644
index 0000000..9b72a26
--- /dev/null
+++ b/test/model/default/classes/first.yml
@@ -0,0 +1,32 @@
+parameters:
+  _param:
+    some: param
+    colour: red
+  lab:
+    name: test
+    label: first
+  colour:
+    escaped: \${_param:colour}
+    doubleescaped: \\${_param:colour}
+    unescaped: ${_param:colour}
+  colours:
+    red:
+      name: red
+    blue:
+      name: blue
+  one:
+    a: 1
+    b: 2
+  two:
+    c: 3
+    d: 4
+  three:
+    e: 5
+  list_to_override:
+  - one
+  - two
+  dict_to_override:
+   one: 1
+   two: 2
+
+
diff --git a/test/model/default/classes/lab/env/dev.yml b/test/model/default/classes/lab/env/dev.yml
new file mode 100644
index 0000000..0cce363
--- /dev/null
+++ b/test/model/default/classes/lab/env/dev.yml
@@ -0,0 +1,4 @@
+
+parameters:
+  lab:
+    name: dev
diff --git a/test/model/default/classes/second.yml b/test/model/default/classes/second.yml
new file mode 100644
index 0000000..dab50c7
--- /dev/null
+++ b/test/model/default/classes/second.yml
@@ -0,0 +1,9 @@
+classes:
+- first
+
+parameters:
+  will:
+    warn:
+      at:
+        second: ${_param:notfound}
+  three: ${one}
diff --git a/test/model/default/classes/third.yml b/test/model/default/classes/third.yml
new file mode 100644
index 0000000..135acd4
--- /dev/null
+++ b/test/model/default/classes/third.yml
@@ -0,0 +1,18 @@
+classes:
+- second
+
+parameters:
+  _param:
+    notfound: exist
+  myparam: ${_param:some}
+  will:
+    not:
+      fail:
+        at:
+          tree: ${_param:notfound}
+  three: ${two}
+  empty:
+    list: []
+    dict: {}
+  ~list_to_override: ${empty:list}
+  ~dict_to_override: ${empty:dict}
diff --git a/test/model/default/nodes/reclass.yml b/test/model/default/nodes/reclass.yml
new file mode 100644
index 0000000..94b7519
--- /dev/null
+++ b/test/model/default/nodes/reclass.yml
@@ -0,0 +1,3 @@
+
+classes:
+- third
diff --git a/test/model/default/reclass-config.yml b/test/model/default/reclass-config.yml
new file mode 100644
index 0000000..9d8f30f
--- /dev/null
+++ b/test/model/default/reclass-config.yml
@@ -0,0 +1 @@
+storage_type: yaml_fs
diff --git a/test/model/extensions/classes/first.yml b/test/model/extensions/classes/first.yml
new file mode 100644
index 0000000..96ece27
--- /dev/null
+++ b/test/model/extensions/classes/first.yml
@@ -0,0 +1,6 @@
+parameters:
+  _param:
+    some: param
+  lab:
+    name: test
+    label: first
diff --git a/test/model/extensions/classes/lab/env/dev.yml b/test/model/extensions/classes/lab/env/dev.yml
new file mode 100644
index 0000000..0cce363
--- /dev/null
+++ b/test/model/extensions/classes/lab/env/dev.yml
@@ -0,0 +1,4 @@
+
+parameters:
+  lab:
+    name: dev
diff --git a/test/model/extensions/classes/second.yml b/test/model/extensions/classes/second.yml
new file mode 100644
index 0000000..a9babd3
--- /dev/null
+++ b/test/model/extensions/classes/second.yml
@@ -0,0 +1,8 @@
+classes:
+- first
+
+parameters:
+  will:
+    warn:
+      at:
+        second: ${_param:notfound}
diff --git a/test/model/extensions/classes/third.yml b/test/model/extensions/classes/third.yml
new file mode 100644
index 0000000..20a937c
--- /dev/null
+++ b/test/model/extensions/classes/third.yml
@@ -0,0 +1,13 @@
+classes:
+- missing.class
+- second
+
+parameters:
+  _param:
+    notfound: exist
+  myparam: ${_param:some}
+  will:
+    not:
+      fail:
+        at:
+          tree: ${_param:notfound}
diff --git a/test/model/extensions/nodes/reclass.yml b/test/model/extensions/nodes/reclass.yml
new file mode 100644
index 0000000..94b7519
--- /dev/null
+++ b/test/model/extensions/nodes/reclass.yml
@@ -0,0 +1,3 @@
+
+classes:
+- third
diff --git a/test/model/extensions/reclass-config.yml b/test/model/extensions/reclass-config.yml
new file mode 100644
index 0000000..6e2f101
--- /dev/null
+++ b/test/model/extensions/reclass-config.yml
@@ -0,0 +1,3 @@
+storage_type: yaml_fs
+ignore_class_notfound: True
+ignore_class_regexp: ['.*']
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..ff5b77e
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,38 @@
+# this file is *not* meant to cover or endorse the use of tox or pytest or
+# testing in general,
+#
+#  It's meant to show the use of:
+#
+#  - check-manifest
+#     confirm items checked into vcs are in your sdist
+#  - python setup.py check (using the readme_renderer extension)
+#     confirms your long_description will render correctly on pypi
+#
+#  and also to help confirm pull requests to this project.
+
+[tox]
+envlist = py{27}
+
+[testenv]
+basepython =
+    py27: python2.7
+whitelist_externals=
+    make
+deps =
+    check-manifest
+    {py27}: readme_renderer
+    # flake8 out of the picture right now
+    pytest
+    mock
+    pylint
+    nose
+commands =
+    check-manifest --ignore tox.ini,tests*
+    {py27}: python setup.py check -m -r -s
+    # flake8 . # FIXME: This code smell check goes poorly for us at present
+    make tests
+    # make lint-errors # FIXME: Cause these to operate properly inside tox
+    # make coverage
+[flake8]
+exclude = .tox,*.egg,build,data
+select = E,W,F