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

  string.Template instances.

Doc/library/string.rst

@@ -640,12 +640,14 @@ 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

@@ -323,6 +323,9 @@ C API
 Documentation
 -------------
 
+- Issue #24351: Clarify what is meant by "identifier" in the context of
+  string.Template instances.
+
 - Issue #22155: Add File Handlers subsection with createfilehandler to tkinter
   doc.  Remove obsolete example from FAQ.  Patch by Martin Panter.