bug#35764: Proposal: gnus-summary-describe-article

["積丹尼 Dan Jacobson" <jidanni@jidanni.org>]

Just like M-x describe-char gives tons of details about a character, a
future gnus-summary-describe-article function could
show all the items in the C-h v gnus-summary-line-format docstring,
one per line, whithout the user needing to change his
gnus-summary-line-format just to see what they all are for one article.
Output would have % escapes helpfully mentioned.

So it would list:

%N          Article number, left padded with spaces (string)
%S          Subject (string)
%s          Subject if it is at the root of a thread, and "" otherwise (string)
%n          Name of the poster (string)
%a          Extracted name of the poster (string)
...

Like this:

Article number %N: 1234
       Subject %S: Larry wants a waffle
        Poster %n: Bill Prfowitz
...

And mention this new function on
(info "(gnus) Back End Interface")

And maybe with a prefix argument just have it analyze the user's current
gnus-summary-line-format, in the order that the %'s appear in it.