def add(self, string: (str, list)):
slot = _SlotFrame(self,<EOL>remove_callback=self._redraw,<EOL>entries=self._slot_columns)<EOL>slot.add(string)<EOL>self._slots.append(slot)<EOL>self._redraw()<EOL>
Add a new slot to the multi-frame containing the string.
:param string: a string to insert
:return: None