'Low-level problem type introspection for content libraries filtering by problem type'

@property
def problem_types(self):

    try:
        tree = etree.XML(self.data)
    except etree.XMLSyntaxError:
        log.error('Error    parsing    problem    types    from    xml    for    capa    module    {}'.format(self.display_name))
        return None
    registered_tags = responsetypes.registry.registered_tags()
    return {node.tag for node in tree.iter() if (node.tag in registered_tags)}
