It's a bit difficult to not get confused by all the layers of metamodelling. So the 'Class' we see here and I have discussed in the last postings is the metaclass of the uml classes (like Class, Association, Property). So each of our instances of class of uml can be extended through stereotypes.
Using stereotypes we can add properties to any metaclass.
To each metaclass, we can define Extensions. An Extension is a specialization of Association connecting two Properties.
There is a special Property called 'ExtensionEnd'.
Through the inheritance chain, ExtensionEnd specializes MultiplicityElement. The behavior is redefined as:
As a TypedElement the Extension End can be of type Classifier, this is restricted (redefined) to Stereotype.
There is a special diagram to draw profiles, the profile diagram. In this we can import uml meta-classes we want to extend (<<metaclass>>), draw the stereotypes (<<Stereotype>>) with Properties and finally relate both with Extensions.
In a profile diagram, the Extension looks very similar to the generalization in a class diagram. In contrast to specializing the meta classes of the uml model to fit our LabVIEW-needs, we can add the properties anywhere in the inheritance chain (e.g. named element) of the reference model.