bpo-36216: Add check for characters in netloc that normalize to separators (GH-12201)

diff --git a/Doc/library/urllib.parse.rst b/Doc/library/urllib.parse.rst
index 913e933..af15f5b 100644
--- a/Doc/library/urllib.parse.rst
+++ b/Doc/library/urllib.parse.rst
@@ -124,6 +124,11 @@
    Unmatched square brackets in the :attr:`netloc` attribute will raise a
    :exc:`ValueError`.
 
+   Characters in the :attr:`netloc` attribute that decompose under NFKC
+   normalization (as used by the IDNA encoding) into any of ``/``, ``?``,
+   ``#``, ``@``, or ``:`` will raise a :exc:`ValueError`. If the URL is
+   decomposed before parsing, no error will be raised.
+
    .. versionchanged:: 3.2
       Added IPv6 URL parsing capabilities.
 
@@ -136,6 +141,10 @@
       Out-of-range port numbers now raise :exc:`ValueError`, instead of
       returning :const:`None`.
 
+   .. versionchanged:: 3.8
+      Characters that affect netloc parsing under NFKC normalization will
+      now raise :exc:`ValueError`.
+
 
 .. function:: parse_qs(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None)
 
@@ -259,10 +268,19 @@
    Unmatched square brackets in the :attr:`netloc` attribute will raise a
    :exc:`ValueError`.
 
+   Characters in the :attr:`netloc` attribute that decompose under NFKC
+   normalization (as used by the IDNA encoding) into any of ``/``, ``?``,
+   ``#``, ``@``, or ``:`` will raise a :exc:`ValueError`. If the URL is
+   decomposed before parsing, no error will be raised.
+
    .. versionchanged:: 3.6
       Out-of-range port numbers now raise :exc:`ValueError`, instead of
       returning :const:`None`.
 
+   .. versionchanged:: 3.8
+      Characters that affect netloc parsing under NFKC normalization will
+      now raise :exc:`ValueError`.
+
 
 .. function:: urlunsplit(parts)