Remove all child elements whose tagname (e.g. 'a:p') appears in
        *tagnames*.

def remove_all(self, *tagnames):
        """
        Remove all child elements whose tagname (e.g. 'a:p') appears in
        *tagnames*.
        """
        for tagname in tagnames:
            matching = self.findall(qn(tagname))
            for child in matching:
                self.remove(child)