Multiple Actors/UIs and Communication Diagrams

In the Robustness Analysis approach (ICONIX) Classes participating in a Communication Diagram are derived from the respective Use Cases. The general proposed architecture of Communication Diagrams incorporates a) One Actor b) One Boundary Class c) One Control Class and d) As many Entity Classes identified in the Use Case
Two questions:

  1. What if the Actor encounters more than one UI during the use case? Is it OK to use 2 Boundary Classes in the same Communication Diagram?
  2. What about depiction of Secondary actors? Are they omitted? (I am asking because I have never seen a Communication Diagram with more than one actor)

Thank you!

Yes, a system can have multiple boundaries.

No, you can have multiple actors.

For me, there are no hard rules with UML as it is already pretty relaxed. If your models will make more sense if you add additional actors or boundary classes, please do so.