How to refer to parsed element in export-filter?

[Thorsten Jolitz <tjolitz@gmail.com>]

Hi List,

in an exporter I would like to have a filter function (for headlines)
that acts conditional on the back-end and on the headline's properties
(say its :todo-keyword). But is it possible to find the internal
representation of the filtered headline in the communication channel?

#+BEGIN_SRC emacs-lisp
  (defun org-xyz-headline-filter (headline back-end info)
    "Filter transcoded output for headlines."
    (when (and (eq back-end 'xyz)
               (member
                (org-element-property
                 :todo-keyword
                 (FIND-CURR-HEADLINE
                  (plist-get info :parse-tree)))
                (org-xyz-keywords)))...))
#+END_SRC

I cannot figure out how to implement 'FIND-CURR-HEADLINE' in the stub
above. Do I have to do the filtering directly in the transcoder function
instead, or is there a way to make references to the element's
parse-tree in a filter function?

-- 
cheers,
Thorsten