docs: def is_admin(controller, client, actor):
      """Used to determine whether someone issuing a command is an admin.
  
      By default, checks to see if there's a line of the type nick=host that
      matches the command's actor in the [admins] section of the config file,
      or a key that matches the entire mask (e.g. "foo@bar" or "foo@bar=1").
      """
      config = controller.config
      if not config.has_section("admins"):
          logging.debug("Ignoring is_admin check - no [admins] config found.")
          return False
      for key,val in config.items("admins"):
          if actor == User(key):
              logging.debug("is_admin: %r matches admin %r", actor, key)
              return True
          if actor.nick.lower() == key.lower() and actor.host.lower() == val.lower():
              logging.debug("is_admin: %r matches admin %r=%r", actor, key, val)
              return True
      logging.debug("is_admin: %r is not an admin.", actor)
      return False