Summary format - the `u' spec

[Harry Putnam <reader@newsguy.com>]

The following message is a courtesy copy of an article
that has been posted to gnu.emacs.gnus as well.


>From gnus info; this looks like it can be made to do what I want.

`u'
     User defined specifier.  The next character in the format string
     should be a letter.  Gnus will call the function
     `gnus-user-format-function-'`X', where `X' is the letter following
     `%u'.  The function will be passed the current header as argument.
     The function should return a string, which will be inserted into
     the summary just like information from any other summary specifier.


Hopefully I'm, correct in thinking the line that says:
"...The function will be passed the current header as argument."
Means that all header lines get scanned.

I want to use this option to cause gnus to scan the headers for 
this pattern `^Keywords: \\[A\\] '.  And if found, to insert the capital
letter found inside the [] into th summary display. 

I think this is fairly simple, maybe but don't really have a clue how
to proceed.

Does someone have an example of using this function in the way I
described?