Hi, I am trying to understand the process_children() function. If in my extension is have def execute(self, context, self_node, input_node, output_parent): self.process_children(context, output_parent) then processing works just fine (although I haven't done anything with the output here). However, using def execute(self, context, self_node, input_node, output_parent): x = self.process_children(context, output_parent=None) output_parent.append(x) crashes: x = self.process_children(context, output_parent=None) File "xsltext.pxi", line 111, in lxml.etree.XSLTExtension.process_children (src/lxml/lxml.etree.c:164356) File "readonlytree.pxi", line 550, in lxml.etree._nonRoNodeOf (src/lxml/lxml.etree.c:78766) TypeError: invalid argument type <class 'NoneType'> although I had assumed the two to be synonymous. I ask because I want to inject my own node and dangle children off of my own node like this: p = lxml.etree.Element("p") p.attrib["style"] = "..." output_parent.append(p) self.process_children(context, p) but that, too, fails. What am I doing wrong here? Thanks! Jens -- Jens Tröger http://savage.light-speed.de/