code: def clear_tab_stop(self, how=0):
          
          if how == 0:
              # Clears a horizontal tab stop at cursor position, if it's
              # present, or silently fails if otherwise.
              self.tabstops.discard(self.cursor.x)
          elif how == 3:
              self.tabstops = set()
docs: Clear a horizontal tab stop.
  
          :param int how: defines a way the tab stop should be cleared:
  
              * ``0`` or nothing -- Clears a horizontal tab stop at cursor
                position.
              * ``3`` -- Clears all horizontal tab stops.