code: public function render($sGlyphicon, array $aGlyphiconAttributes = null)
      {
          if (!is_scalar($sGlyphicon)) {
              throw new InvalidArgumentException('Glyphicon expects a scalar value, "' . gettype($sGlyphicon) . '" given');
          }
  
          if (empty($aGlyphiconAttributes)) {
              $aGlyphiconAttributes = array('class' => 'glyphicon');
          } else {
  
              if (empty($aGlyphiconAttributes['class'])) {
                  $aGlyphiconAttributes['class'] = 'glyphicon';
              } elseif (!preg_match('/(\s|^)glyphicon(\s|$)/', $aGlyphiconAttributes['class'])) {
                  $aGlyphiconAttributes['class'] .= ' glyphicon';
              }
          }
  
          if (strpos('glyphicon-', $sGlyphicon) !== 0) {
              $sGlyphicon = 'glyphicon-' . $sGlyphicon;
          }
  
          if (!preg_match('/(\s|^)' . preg_quote($sGlyphicon, '/') . '(\s|$)/', $aGlyphiconAttributes['class'])) {
              $aGlyphiconAttributes['class'] .= ' ' . $sGlyphicon;
          }
  
          return sprintf(
              static::$glyphiconFormat,
              $this->createAttributesString($aGlyphiconAttributes)
          );
      }
docs: Retrieve glyphicon markup
  @param string $sGlyphicon
  @param  array $aGlyphiconAttributes : [optionnal]
  @throws InvalidArgumentException
  @return string