How to get the value of an element's multiple property?

Question

1C-Bitrix

There is a multiple property "region". In which you can select several cities.
I found an example of displaying a property value here: https://dev.1c-bitrix.ru/api_help/iblock/classes/c...

The code works successfully:

$db_props = CIBlockElement::GetProperty($arItem['IBLOCK_ID'], $arItem['ID'], "sort", "asc", array());

  $PROPS = array();

  while( $ar_props = $db_props->GetNext() )
    $PROPS[$ar_props['CODE']] = $ar_props['VALUE_ENUM'];

..but outputs only the last value of the multiple property.

The example above uses the IKSO_CUSTOM:: class. But when I add this class I get an error:

[Error] 
Class 'IKSO_CUSTOM' not found (0)..

How to be?