protected function setExtending( Line$firstLine ):self
	{
		switch( $name= $firstLine->pregGet('/(?<=^@)[\w-:]+/') ){
			default:{
				$this->throw("The @$name is not supported.");
			}break;
			case 'extend':{
				$this->extend($firstLine->pregGet('/(?<=\( ).*(?= \))/'));
			}break;
			case 'show':
			case 'include':
			case 'section':{
				$this->throw("The @$name can not be used on first line.");
			}break;
		}

		return $this;
	}