- Issue #24351: Clarify what is meant by "identifier" in the context of

  string.Template instances.

Doc/library/string.rst

@@ -644,12 +644,14 @@ Instead of the normal ``%``\ -based substitutions, Templates support ``$``\
 * ``$$`` is an escape; it is replaced with a single ``$``.
 
 * ``$identifier`` names a substitution placeholder matching a mapping key of
-  ``"identifier"``.  By default, ``"identifier"`` must spell a Python
-  identifier.  The first non-identifier character after the ``$`` character
-  terminates this placeholder specification.
-
-* ``${identifier}`` is equivalent to ``$identifier``.  It is required when valid
-  identifier characters follow the placeholder but are not part of the
+  ``"identifier"``.  By default, ``"identifier"`` is restricted to any
+  case-insensitive ASCII alphanumeric string (including underscores) that
+  starts with an underscore or ASCII letter.  The first non-identifier
+  character after the ``$`` character terminates this placeholder
+  specification.
+
+* ``${identifier}`` is equivalent to ``$identifier``.  It is required when
+  valid identifier characters follow the placeholder but are not part of the
   placeholder, such as ``"${noun}ification"``.
 
 Any other appearance of ``$`` in the string will result in a :exc:`ValueError`

Misc/NEWS

@@ -45,6 +45,12 @@ Tests
   tp_finalize to avoid reference leaks encountered when combining tp_dealloc
   with PyType_FromSpec (see issue #16690 for details)
 
+Documentation
+-------------
+
+- Issue #24351: Clarify what is meant by "identifier" in the context of
+  string.Template instances.
+
 
 What's New in Python 3.5.0 beta 2?
 ==================================