Nested focus of control in sequence diagrams

[Chuck]

Hello,
Currently evaluating EA, and want to see if the tool supports nested threads in sequence diagrams, when the thread is not a self call.

Consider the following: A calls B (step 1).  Before returning, B calls C (step 2).  Now, I want to indicate that at second thread, say from D, calls B between step 1 and 2, causing a nested focus of control.

Can't figure out how to do it, is this type of feature present in the tool?

Thanks,
Chuck