static function checkPath($path, $constraints, $helper) {
    list($where, $path) = explode(':', $path);

    if (empty($constraints)) $constraints = ['required' => TRUE];

    foreach ($constraints as $con => $params) {
      if ($con === 'required') $constraints['required'] = $path;

      elseif ($con === 'in')   $constraints['in'] = [[$path, $params]]; // !REM!:  params for Valitron rule in indexed array.

      else unset($constraints[$con]); 
    }


    return self::is($helper[$where], $constraints);
  }