Issue #22088: Port base64 character ignoring doc and test from 857d9fe60169
diff --git a/Doc/library/base64.rst b/Doc/library/base64.rst
index 2a9840b..e346efb 100644
--- a/Doc/library/base64.rst
+++ b/Doc/library/base64.rst
@@ -45,9 +45,9 @@
    length 2 (additional characters are ignored) which specifies the alternative
    alphabet used instead of the ``+`` and ``/`` characters.
 
-   The decoded string is returned.  A :exc:`TypeError` is raised if *s* were
-   incorrectly padded or if there are non-alphabet characters present in the
-   string.
+   The decoded string is returned.  A :exc:`TypeError` is raised if *s* is
+   incorrectly padded.  Non-base64-alphabet characters are
+   discarded prior to the padding check.
 
 
 .. function:: standard_b64encode(s)