concurrency in interaction diagrams

[RonaldTrivera]

Hi all,

I cant find in anyways the option to define threaded behaviour in communication diagrams, by being able to add letters to my message numbers like this 1.1a & 1.1b
Also in the sequence diagrams i dont see options to create thick borders on instances to indicate they are threaded.
Am i missing something here or are there other ways to illustrate this?

with kind regards,
Ronald