@classmethod
def explain_tags(cls, body):
    """ return usage string containing tag names, formats """
    s = """
            lightswitch:offhours=21:00-7:00
            lightswitch:offhours=21:00-23:00

            lightswitch:offmode=toggle
            lightswitch:offmode=offonly

            lightswitch:offdays=sat,sun
            lightswitch:offdays=monday
        """
    return s
