public function toggle( $token, $force = null )
	{
		$output   = null;
		$contains = $this->contains( $token );

		if ( $contains ) {
			if ( ! $force ) {
				$this->__remove( [ $token ] );
				$change = false;
			}
			else {
				$change = true;
			}
		}
		else {
			if ( false === $force ) {
				$change = false;
			}
			else {
				$this->__add( [ $token ] );
				$change = true;
			}
		}

		return $change;
	}