docs: def register_flags(self, flags):
          """
          Register flags as being relevant to this handler.
  
          Relevant flags will be used to determine if the handler should
          be re-invoked due to changes in the set of active flags.  If this
          handler has already been invoked during this :func:`dispatch` run
          and none of its relevant flags have been set or removed since then,
          then the handler will be skipped.
  
          This is also used for linting and composition purposes, to determine
          if a layer has unhandled flags.
          """
          self._CONSUMED_FLAGS.update(flags)
          self._flags.update(flags)