public function addSeries( $seriesOrArray )
	{
	    if (! is_array( $seriesOrArray ) ) {
	        $seriesOrArray = array( $seriesOrArray );
	    }
	    
	    if ( is_array( $seriesOrArray ) ) {
	        foreach ( $seriesOrArray as $series ) 
	        {
	            if (! $series instanceof Series ) {
	                throw new \UnexpectedValueException( '\Altamira\Chart::addSeries expects a single series or an array of series instances' );
	            } 
	            $this->addSingleSeries( $series );
	        }
	    }
	    
	    return $this;
	}