code: private function assert($value, $word = '')
      {
          if ($value) {
              if ($this->not) {
                  throw new \Exception(
                      empty($word)
                      ? 'Field contain a value, but should not.'
                      : "Element is $word, but should not be."
                  );
              }
          } else {
              if (!$this->not) {
                  throw new \Exception(
                      empty($word)
                      ? 'Field does not contain a value.'
                      : "Element is not $word."
                  );
              }
          }
      }
docs: @param bool $value
  Value for checking.
  @param string $word
  A word for default message (e.g. "checked", "selected", etc).
  
  @throws \Exception