Fix docstring of sphinx.util.parsing.nested_parse_to_nodes() (#14054)

Author: gmilde

sphinx/util/parsing.py

@@ -39,8 +39,7 @@ def nested_parse_to_nodes(
         Note that this option bypasses Docutils' usual checks on
         doctree structure, and misuse of this option can lead to
         an incoherent doctree. In Docutils, section nodes should
-        only be children of ``Structural`` nodes, which includes
-        ``document``, ``section``, and ``sidebar`` nodes.
+        only be children of ``document`` or ``section`` nodes.
     :param keep_title_context:
         If this is False (the default), then *content* is parsed as if it were
         an independent document, meaning that title decorations (e.g. underlines)
@@ -50,6 +49,10 @@ def nested_parse_to_nodes(
         If this is True, then title underlines must match those in
         the surrounding document, otherwise the behaviour is undefined.
 
+        Warning: Up to Docutils 0.21, sections with a decoration style
+        matching a level that is higher than the current section level are
+        silently discarded! Since Docutils 0.22.1, an error is reported.
+
     .. versionadded:: 7.4
     """
     document = state.document