Limit to recipient?

[Graham Todd <gtodd@yorku.ca>]

Hi all,

I have this im my ~/.gnus to make the Summary buffers in my sent-mail
archives more meaningful:


(setq gnus-extra-headers
           '(To Newsgroups))
(setq nnmail-extra-headers gnus-extra-headers)
(setq gnus-summary-line-format
          "%U %d%R%z%I%(%[%4L: %-20,20f%]%) %s\n")
(setq gnus-ignored-from-addresses
           "Graham Todd")


I'd like to be able to add a "limit" function something like this:

(defun gnus-summary-limit-to-recipient (????)
  "Limit the summary buffer to articles that were sent to a recipient
  that matches a regexp." 
 (interactive "sLimit to recipient (regexp): ")
  (gnus-summary-limit-to-subject ???? "????"))

but what would I have to substitute for the ???? above. Theres a few
line in gnus-sum.el like this:

(unless (fboundp (intern (concat "mail-header-" header)))
      (error "%s is not a valid header" header))

which seem to prevent gnus-extra-headers like "To" or "Newsgroups"
from being seen as valid headers. How and where could they be defined
as valid headers so a defun like gnus-summary-limit-to-recipient would
work?

-- 
Graham Todd