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