Does not work as expected. @seidewitz, please confirm is our sample is correct.

part def C;
attribute def S;

metadata def <m> M :> Metaobjects::SemanticMetadata {
  :> annotatedElement : SysML::PartDefinition;
  :> annotatedElement : SysML::AttributeDefinition;
  :>> baseType = 
      if annotatedElement istype SysML::PartDefinition ? 
          C meta SysML::PartDefinition else S meta SysML::AttributeDefinition;
}

#m part def tPart;
#m attribute def tAttribute;

@gke3
The sample is correct, and it works for me, both in the Eclipse and Jupyter deployments of 2025-10.

Try this:

part p {
    protected attribute x;
}
attribute y = p.x; // ERROR:Couldn't resolve reference to Element 'x'.

If you don't get an error, then you don't have 2025-10 installed.

@seidewitz
Howdy,
You were right, the installation had a problem that it had several versions of the components deployed. Once we reinstalled from a clean slate, it started to work.
It seems to work properly - we tried both a simple type test condition and slightly more complicated ones (such as if annotatedElement.isComposite).
Congrats; this one is done.
Now UAFv2 can move on - till they run into their more complicated cases (the ones requiring more complex conditions, model level evaluable tweaking etc)