registering functions or templates

Hi,

I've seen that all DOM extension use the PHP stream wrappers. I was 
asking myself if it was possible to register a PHP function for future 
use in Xpath, or register a function for future use as a template in XSLT.

Such functionnality is already present in the python module based on 
libxml : see http://xmlsoft.org/python.html at the title "xpathext.py"

I do not see such thing, neither in presentation slides neither in 
examples or tests in snaps.

Is this feature planned ?
If no : what about making it aviable ? what are the problems ?
If yes : do you plan to release it for the first release of php5 or later ?

Thanks
-- 
Eric