diff --git a/doc/source/operations.rst b/doc/source/operations.rst
index a157403..4801803 100644
--- a/doc/source/operations.rst
+++ b/doc/source/operations.rst
@@ -97,6 +97,12 @@
 define all nodes (and if only to allow them to be enumerated for the
 inventory).
 
+The mapped classes can also contain backreferences when regular expressions
+are used, although they need to be escaped, e.g.::
+
+  class_mappings:
+    - /\.(\S+)$/ tld-\\1
+
 Parameter interpolation
 ------------------------
 Parameters may reference each other, including deep references, e.g.::
diff --git a/doc/source/todo.rst b/doc/source/todo.rst
index 446dd59..3899ec0 100644
--- a/doc/source/todo.rst
+++ b/doc/source/todo.rst
@@ -29,16 +29,6 @@
 people understand what's going on, where data are being changed/merged, and to
 help solve problems.
 
-Mapping interpolation
----------------------
-Given class mappings, it should be possible to use references in the classes,
-e.g.:
-
-    /\.(\S+)$/ → in-domain-\1
-
-such that a host like ``example.org`` would get the class ``in-domain-org``
-assigned to it.
-
 Data from CMS for interpolation
 -------------------------------
 Depending on the CMS in question, it would be nice if |reclass| had access to