PMA\libraries\Util::requestString PHP Method

    public static function requestString($value)
    {
        while (is_array($value) || is_object($value)) {
            $value = reset($value);
        }
        return trim((string) $value);
    }

 /**
  * Validates value according to given regular expression
  * Pattern and modifiers must be a valid for PCRE <b>and</b> JavaScript RegExp
  *
  * @param string $path   path to config
  * @param array  $values config values
  * @param string $regex  regular expression to match
  *
  * @return array
  */
 public static function validateByRegex($path, $values, $regex)
 {
     if (!isset($values[$path])) {
         return '';
     }
     $result = preg_match($regex, Util::requestString($values[$path]));
     return array($path => $result ? '' : __('Incorrect value!'));
 }