How to access xmlParserCtxt structure from within xmlSAXHandler callbacks?

Question

I'm parsing (X)HTML pages content with libxml using the following call:

htmlDocPtr doc = htmlSAXParseDoc(content, NULL, &html_handler, NULL);

But for debugging purposes I need to analyze some of the current node properties in the start/end element callbacks. I know that the fourth argument of htmlSAXParseDoc can be used to pass any user defined data to the callbacks, but I don't have a pointer to xmlParserCtxt.