code: private static function buildAttribArrayVal($key, $value = array())
      {
          if ($key == 'class') {
              if (!\is_array($value)) {
                  $value = \explode(' ', $value);
              }
              $value = \array_filter(\array_unique($value));
              \sort($value);
              $value = \implode(' ', $value);
          } elseif ($key == 'style') {
              $keyValues = array();
              foreach ($value as $k => $v) {
                  $keyValues[] = $k.':'.$v.';';
              }
              \sort($keyValues);
              $value = \implode('', $keyValues);
          } else {
              $value = null;
          }
          return $value;
      }
docs: Convert array attribute value to string
  
  Convert class/style array value to string
  This function is not meant for data attributs
  
  @param string $key   attribute name (class|style)
  @param array  $value classnames for class, key/value for style
  
  @return string