Porting from XEmacs to Emacs: event-glyph-extent

["Achim D. Brucker" <brucker@spamfence.net>]

Hi,   
is there an howto about porting elisp-code from XEmacs to GNU Emacs?
      
At the moment I'm trying to port an (unmainted) XEmacs mode to GNU 
Emacs 21.3. With the help of lucid.el and looking into various (X)Emacs 
modes I got most of the stuff working, but now I'm getting stuck with the 
following routine:
       
(defun zeta-marker-activate (e)
  (interactive "e")
    (let ((m (event-glyph-extent e)) act)
        (if (and m (setq act (extent-property m 'zeta-marker-action)))
                (funcall act m)
         (mouse-set-point e))))
      
"event-glyph-extent" seems to be problematic, at least my attempts to
emulate this in GNU Emacs (with constructs like "overlays-at
(event-start e)")
failed. Is this non-trivial or do I just missing something obvious?
       
Achim