function TreeIdentifierRule($field_name, $parent_node_id, $node_id = TREE_IDENTIFIER_RULE_UNKNOWN_NODE_ID)
  {
    $this->node_id = $node_id;
    $this->parent_node_id = $parent_node_id;

    parent :: SingleFieldRule($field_name);
  }
  function LocaleDateRule($fieldname, $locale_id = '')
  {
    if (!$locale_id &&  !defined('CONTENT_LOCALE_ID'))
      $this->locale_id = DEFAULT_CONTENT_LOCALE_ID;
    elseif(!$locale_id)
      $this->locale_id = CONTENT_LOCALE_ID;
    else
      $this->locale_id = $locale_id;

    parent :: SingleFieldRule($fieldname);
  }
  function UniqueUserRule($field_name, $current_identifier='')
  {
    $this->current_identifier = $current_identifier;

    parent :: SingleFieldRule($field_name);
  }
  function InvalidValueRule($field_name, $invalid_value)
  {
    $this->invalid_value = $invalid_value;

    parent :: SingleFieldRule($field_name);
  }
  function UniqueUserEmailRule($field_name, $email='')
  {
    $this->current_email = $email;

    parent :: SingleFieldRule($field_name);
  }