I am not really sure to which part this belongs to.

Issue:
In the services a method call can only return StatusCodes defined by the OPC UA specification. This is often not enough and more detailed status for the specific method is desired. An often-used pattern is therefore to return a StatusCode as out parameter of the method (e.g. in FDI).

What I did not found anywhere I looked was the handling of such methods in the service call. Do we need to return a Good StatusCode on the services and then a user-defined method StatusCode that could indicate that the method failed? Can I even access the out parameters when the method returns a BAD status code on the service and expect anything useful in them?

From my point of view it is desirable to define in the base specs (therefore I had chosen Part 3) at least a pattern that should be used to return Method-specific status codes and what is the expected behavior for on the service level.

For this case it would also be good if the out variable can be an “extendable enum”, meaning not a specific Enum DataType (which cannot be extended) but something having EnumStrings or EnumValues so that standard information models can define some base status but vendors can extend that. As I understood proving such a feature is already in discussion anyhow.