protected function parseFirstLine():self
	{
		$line= $this->getLine();

		if( '@'===$line->getChar(0) ){
			return $this->setExtending($line);
		}

		$this->docType= $line->content;
		$docTypeContent= $this->getConfig('doc_types') or $this->throw("DocType $this->docType is not supported");

		$this->indentation= $this->htsl->getConfig('indentation',$this->docType) ?? ( function( $scalarOrFalse ){ return is_scalar($scalarOrFalse)?$scalarOrFalse:false; } )($this->htsl->getConfig('indentation'));

		return $this->appendLine($docTypeContent);
	}