Combine the focus edit widget with the one below.

def combine_focus_with_next(self):
        """Combine the focus edit widget with the one below."""

        below, ignore = self.get_next(self.focus)
        if below is None:
            # already at bottom
            return

        focus = self.lines[self.focus]
        focus.set_edit_text(focus.edit_text + below.edit_text)
        del self.lines[self.focus + 1]