Contao\ImageSize::validator PHP Method

    protected function validator($varInput)
    {
        $this->import('BackendUser', 'User');
        $varInput[0] = parent::validator($varInput[0]);
        $varInput[1] = parent::validator($varInput[1]);
        $varInput[2] = preg_replace('/[^a-z0-9_]+/', '', $varInput[2]);
        $imageSizes = \System::getContainer()->get('contao.image.image_sizes');
        $this->arrAvailableOptions = $this->User->isAdmin ? $imageSizes->getAllOptions() : $imageSizes->getOptionsForUser($this->User);
        if (!$this->isValidOption($varInput[2])) {
            $this->addError(sprintf($GLOBALS['TL_LANG']['ERR']['invalid'], $varInput[2]));
        }
        return $varInput;
    }

 /**
  * Trim values
  * @param   mixed
  * @return  mixed
  */
 protected function validator($varInput)
 {
     $validatedInput = parent::validator($varInput);
     $validatedInput[2] = preg_replace('/[^a-z0-9_%]+/', '', $varInput[2]);
     return $validatedInput;
 }