code: func (c *CheckBox) SetAllow3State(enable bool) {
  	if !enable && c.state == 2 {
  		c.state = 0
  	}
  	c.allow3state = enable
  }
docs: // SetAllow3State sets if ComboBox should use 3 states. If the current
  // state is unknown and one disables Allow3State option then the current
  // value resets to off