I believe URL_REGEX is missing a `|`

comparing the 'URL_REGEX explanation comment':

# (__ |`{{2}}|`\w[\w. :\n]*|\.\. _?[\w. :]+|')? is used to find in-line links that

to the actual first line of the regex:

    rf"(__ |`{{2}}|`\w[\w :#\n]*[.|\.\. _?[\w. :]+|')?<?"

the actual regex seems to be 'missing' a | between:

`\w[\w :#\n]*

and

[.|\.\. _?[\w. :]+

This seems to have been removed in https://github.com/PyCQA/docformatter/pull/213 , which doesn't seem intentional to me, as it doesn't seem obviously related to the change that PR was trying to fix (although it's possible I'm misunderstanding here, sorry if so!).

I think this does affect the wrapping behaviour - links in the format starting with .. seem to not get wrapped (although I'm not 100% sure I've understand the expected behaviour). A file with these contents:

def some_func():
    """This is a func.

    A description line.

    This is a very very very very very very very very very very very long line .. _a link reference:  https://domain.invalid/
    """
    pass

def another_func():
    """This is a func.

    A description line.

    .. _a link reference that is very very very very very very very very very very very very very ver longy:  https://domain.invalid/
    """
    pass

def some_func_other_link():
    """This is another func.

    This is a very very very very very very very very very very very long line `A link reference <https://domain.invalid/>`_
    """
    pass

produces this output when docformatter is run over it, only reformatting the link with a different format:

--- before/test_url_regex.py
+++ after/test_url_regex.py
@@ -19,7 +19,9 @@
 def some_func_other_link():
     """This is another func.

-    This is a very very very very very very very very very very very long line `A link reference <https://domain.invalid/>`_
+    This is a very very very very very very very very very very very
+    long line
+    `A link reference <https://domain.invalid/>`_
     """
     pass

I think maybe this isn't obvious/impactful because this kind of link is 'explicit markup' that according to ReST can only start a line of ReST, so it's probably infrequent that you get a link and reference long enough that this would reformat it anyway.

Start in src/docformatter/syntax.py by comparing the URL_REGEX explanation comment with the regex's first line, especially the alternatives around \w[\w :#\n]* and [.|\.\. _?[\w. :]+. Reproduce the wrapping behavior with the provided docstring examples, then add or update a regression test such as test_url_regex.py and confirm the expected link formatting.