Issue #19814: Clarify argparse's docs w.r.t prefix matching
diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index 0b18c6d..b686c44 100644
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -1371,12 +1371,14 @@
>>> parser.parse_args(['--', '-f'])
Namespace(foo='-f', one=None)
+.. _prefix-matching:
-Argument abbreviations
-^^^^^^^^^^^^^^^^^^^^^^
+Argument abbreviations (prefix matching)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The :meth:`~ArgumentParser.parse_args` method allows long options to be
-abbreviated if the abbreviation is unambiguous::
+abbreviated to a prefix, if the abbreviation is unambiguous (the prefix matches
+a unique option)::
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('-bacon')
@@ -1852,6 +1854,12 @@
>>> parser.parse_known_args(['--foo', '--badger', 'BAR', 'spam'])
(Namespace(bar='BAR', foo=True), ['--badger', 'spam'])
+.. warning::
+ :ref:`Prefix matching <prefix-matching>` rules apply to
+ :meth:`parse_known_args`. The parser may consume an option even if it's just
+ a prefix of one of its known options, instead of leaving it in the remaining
+ arguments list.
+
Customizing file parsing
^^^^^^^^^^^^^^^^^^^^^^^^