protected function throwNewInvalidArgumentException ($errorMsg) {
		$selfClass = version_compare(PHP_VERSION, '5.5', '>') ? self::class : __CLASS__;
		$str = '['.$selfClass.'] ' . $errorMsg . ' (';
		if ($this->form) {
			$str .= 'form id: `'.$this->form->GetId() . '`, '
				. 'form type: `'.get_class($this->form).'`, ';
		}
		$str .= 'field type: `'.get_class($this) . '`)';
		throw new \InvalidArgumentException($str);
	}