public function inc($name, $value = 1, $emulate = null)
  {
    $name = $this->get_field_name($name);
    if(isset($this->_operations['$inc'][$name]))
    {
      $this->_operations['$inc'][$name] += $value;
    }
    else
    {
      $this->_operations['$inc'][$name] = $value;
    }
    if ($emulate === FALSE || ($emulate === null && $this->_emulate === FALSE))
    {
      return $this->_set_dirty($name);
    }
    else
    {
      $ref = & $this->get_field_reference($name, TRUE, 0);
      $ref += $value;
      return $this;
    }
  }