/**
  * Called to validate registration form field
  * @return string
  */
 public static function validate_registration_form($id = null, $redirect = null)
 {
     // if registration form have been submitted process it
     // filter to change registration submit button name to avoid validation for forms on same page
     $submit_name = apply_filters('pp_registration_submit_name', 'reg_submit', $id);
     if (isset($_POST[$submit_name])) {
         $register_the_user = ProfilePress_Registration_Auth::register_new_user($_POST, $id, $_FILES, $redirect);
     }
     // display form generated messages
     if (!empty($register_the_user)) {
         $registration_errors = html_entity_decode($register_the_user);
     } else {
         $registration_errors = '';
     }
     return $registration_errors;
 }