A (cx, cy) 2-tuple representing the effective rendering area for text
        within this text frame when margins are taken into account.

def _extents(self):
        """
        A (cx, cy) 2-tuple representing the effective rendering area for text
        within this text frame when margins are taken into account.
        """
        return (
            self._parent.width - self.margin_left - self.margin_right,
            self._parent.height - self.margin_top - self.margin_bottom
        )