def cursor_back(self, count=None):
        """Move cursor left the indicated # of columns. Cursor stops
        at left margin.

        :param int count: number of columns to skip.
        """
        # Handle the case when we've just drawn in the last column
        # and would wrap the line on the next :meth:`draw()` call.
        if self.cursor.x == self.columns:
            self.cursor.x -= 1

        self.cursor.x -= count or 1
        self.ensure_hbounds()