'Clears a horizontal tab stop in a specific way, depending
on the ``type_of`` value:
* ``0`` or nothing -- Clears a horizontal tab stop at cursor
position.
* ``3`` -- Clears all horizontal tab stops.'

def clear_tab_stop(self, type_of=None):

    if (not type_of):
        self.tabstops.discard(self.cursor.x)
    elif (type_of == 3):
        self.tabstops = set()
