def tab(self):
        """Move to the next tab space, or the end of the screen if there
        aren't anymore left.
        """
        for stop in sorted(self.tabstops):
            if self.cursor.x < stop:
                column = stop
                break
        else:
            column = self.columns - 1

        self.cursor.x = column
Move to the next tab space, or the end of the screen if there
        aren't anymore left.