gh-91156: Document how TextIOWrapper interacts with UTF-8 mode (GH-132885)

Document how TextIOWrapper interacts with UTF-8 mode
(cherry picked from commit 245cd6c53278006fa34fd7799d32f0884eb7e75d)

Co-authored-by: Malcolm Smith <smith@chaquo.com>

diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index f793d7a7ef9a84cbcc887b3fcc35acd65579361c..cca9b8bf869f2ac8fa54a67f5bad6fb61388231a 100644 (file)
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -950,7 +950,8 @@ Text I/O
    :class:`TextIOBase`.
 
    *encoding* gives the name of the encoding that the stream will be decoded or
-   encoded with.  It defaults to :func:`locale.getencoding`.
+   encoded with.  In :ref:`UTF-8 Mode <utf8-mode>`, this defaults to UTF-8.
+   Otherwise, it defaults to :func:`locale.getencoding`.
    ``encoding="locale"`` can be used to specify the current locale's encoding
    explicitly. See :ref:`io-text-encoding` for more information.