After attempting Excape x rmail-summary-by-regexp what does it mean when you get... You must set `rmail-search-mime-header-function'

After attempting Excape x rmail-summary-by-regexp what does it mean when you get... You must set `rmail-search-mime-header-function'

[Don Saklad]

          After attempting Escape Control-s what does it mean when you get...
          You must set `rmail-search-mime-header-function'
     
     That you are running a too old Emacs version (23.x, right?).  Time to
     upgrade, this problem is fixed in Emacs 24.
     Alternatively, change this fragment from rmailsum.el:
       (if rmail-enable-mime
           (if rmail-search-mime-header-function
               (funcall rmail-search-mime-header-function msg regexp (point))
             (error "You must set `rmail-search-mime-header-function'"))
         (re-search-forward regexp nil t)))
     to say this instead:
       (if (and rmail-enable-mime
                rmail-search-mime-header-function)
           (funcall rmail-search-mime-header-function msg regexp (point))
         (re-search-forward regexp nil t)))
     and then recompile rmailsum.el and reload rmailsum.elc.


Trying to do that isn't a familiar thing for neophytes, or even for intermediate types!... a?) Any easier, simpler way to handle it when you get
You must set `rmail-search-mime-header-function'

b?) After attempting Escape x rmail-summary-by-regexp what does it mean when you get...
You must set `rmail-search-mime-header-function'