function getMultiValuePropertyDescriptors() {
		$result = array(); // anwering reference to unset var may crash php
		$props =& $this->refPropertyDescriptors();
		reset($props);
		foreach ($props as $name => $prop) {
			if ($prop->isMultiValue())
				$result[$name] = $prop;
		}
		return( $result );
	}