Improve documentation

Author: StanFromIreland

Doc/library/tarfile.rst

@@ -1107,6 +1107,10 @@ reused in custom filters:
     paths (in case the name is absolute
     even after stripping slashes, e.g. ``C:/foo`` on Windows).
     This raises :class:`~tarfile.AbsolutePathError`.
+  - Normalize filenames (:attr:`TarInfo.name`) that contain ``..`` components
+    using :func:`os.path.normpath`.
+    Note that this removes internal ``..`` components, which may change the
+    meaning of the name if it traverses symbolic links.
   - :ref:`Refuse <tarfile-extraction-refuse>` to extract files whose absolute
     path (after following symlinks) would end up outside the destination.
     This raises :class:`~tarfile.OutsideDestinationError`.
@@ -1115,6 +1119,10 @@ reused in custom filters:
 
   Return the modified ``TarInfo`` member.
 
+  .. versionchanged:: next
+
+     Filenames containing ``..`` components are now normalized.
+
 .. function:: data_filter(member, path)
 
   Implements the ``'data'`` filter.