This is especially true for method arguments. If structures used in methods typically concrete types are meant and polymorphic datatypes are the exception.
We need to extend the argument description to add the information 'InlcudeSubTypes', which by default should be False. (This is similar to other places like e.g. Browse service, where we can specify if subtypes of a ReferenceType should be followed too).

This has a big impact on generating methods stubs, especially on non-object-oriented languages like C. The programmer expects a method signature like e.g.

int method_add(struct vector *a, struct vector *b, struct vector *sum);

If the arguments are polymorphic by default we cannot use this kind of methods signature, instead, the programmer must deal with complex extensionobject structures, which are hard to use.
So it is better to have this only for the rare cases where polymorphic types are expected and not for the normal case.

Should be clarified in Part 3.

UA Working Group discussion

We could add an access level flag to a Variable to indicate if subtypes of the DataType are allowed. name could be 'allowSubDataTypes'
This flag is not applicable to abstract types only concrete types.
This can be applied to methods by using the method meta data.
This can be applied to event fields as there are just variables.
When subtyping a variable the datatype is sealed and can not be changed.
The default behavior, when the access level flag is not there, is to not allow subtypes of the DataType. We did not agree the default should be not allow.

Added new Field 'NoSubDataTypes' to AccessLevelExType which indicates a Variable’s ability to SubType its DataType in 8.58

Add NoSubDataTypes bit = 0x800.

agreed to changes in telecon.