CustomPropertyItemID translates the passed CustPropIndex to an TdOPCItem.ItemID.
Many OPC Alarm & Event servers are associated with OPC Data Access servers. While these servers may provide a data access interface to some or all of the attributes associated with events, applications need the ability to determine this specific TdOPCItem.ItemID. For this procedure an associated ServerClsID must be provided in order to be able to access the attribute via the data access interface. This function will be useful in the case the client wishes to use the OPC Data Access interface to subscribe to real-time data associated with a given event or alarm.