Combine the focus edit widget with the one above.

def combine_focus_with_prev(self):
        """Combine the focus edit widget with the one above."""

        above, ignore = self.get_prev(self.focus)
        if above is None:
            # already at the top
            return

        focus = self.lines[self.focus]
        above.set_edit_pos(len(above.edit_text))
        above.set_edit_text(above.edit_text + focus.edit_text)
        del self.lines[self.focus]
        self.focus -= 1