protected function prefixJustifyContent( $value, $extra = null )
  {
    $prop = array(
        '-webkit-justify-content',
        '-ms-flex-pack',
        'justify-content'
    );

    $val[] = $value;
    switch( $value )
    {
      case 'flex-start':
        $val[] = 'start';
        break;
      case 'flex-end':
        $val[] = 'end';
        break;
      case 'space-between':
        $val[] = 'justify';
        break;
      case 'space-around':
        $val[] = 'distribute';
        break;
      default:
        $val[] = $value;
    }
    $val[] = $value;

    return $this->getPrefixRules( $prop, $val, $extra );
  }