public function addIdref($id, $liner = 'yes', array $properties = [] ){
		$itemref = $this->dom->spine->addChild('itemref');
		$itemref['idref'] = $id;
		if( 'no' === $liner ){
			$itemref['linear'] = 'no';
		}
		if( !empty($properties) ){
			$itemref['properties'] = implode(' ', $properties);
		}
		return $itemref;
	}
public function addIdref($id, $liner = 'yes', array $properties = [] ){
		$itemref = $this->dom->spine->addChild('itemref');
		$itemref['idref'] = $id;
		if( 'no' === $liner ){
			$itemref['linear'] = 'no';
		}
		if( !empty($properties) ){
			$itemref['properties'] = implode(' ', $properties);
		}
		return $itemref;
	}
public function addIdref ( $ id , $ liner = 'yes' , array $ properties = [ ] ) { $ itemref = $ this -> dom -> spine -> addChild ( 'itemref' ) ; $ itemref [ 'idref' ] = $ id ; if ( 'no' === $ liner ) { $ itemref [ 'linear' ] = 'no' ; } if ( ! empty ( $ properties ) ) { $ itemref [ 'properties' ] = implode ( ' ' , $ properties ) ; } return $ itemref ; }
Add item ref to spine

@param string $id
@param string $liner
@param array $properties List of property. 'page-spread-left' or 'page-spread-right' is allowed.

@return mixed
Add item ref to spine