'Interpret the parsed XML in `node`, creating an XModuleDescriptor.'

@classmethod
def parse_xml(cls, node, runtime, keys, id_generator):

    if (cls.from_xml != XmlDescriptor.from_xml):
        return super(XmlParserMixin, cls).parse_xml(node, runtime, keys, id_generator)
    else:
        return super(XmlDescriptor, cls).parse_xml(node, runtime, keys, id_generator)
