def issubset(self, other):
        """
        Check if the contents of `self` is a subset of the contents of
        `other.`

        Args:
            other (:class:`FrameSet`):

        Returns:
            bool:
            :class:`NotImplemented`: if `other` fails to convert to a :class:`FrameSet`
        """
        other = self._cast_to_frameset(other)
        if other is NotImplemented:
            return NotImplemented
        return self.items <= other.items
Check if the contents of `self` is a subset of the contents of
        `other.`

        Args:
            other (:class:`FrameSet`):

        Returns:
            bool:
            :class:`NotImplemented`: if `other` fails to convert to a :class:`FrameSet`