Say I want to fly KUL-LHR-ARN on BA, returning a week later. Then I buy a separate ticket, also from BA for ARN-LHR-LAX and return, nested inside the other itinerary. I will not be combining the tickets. Even though the tickets aren't combined, are they considered end-to-end (not allowed), or simply a side trip (allowed).

I'm posting the question here because it seems generic within IATA.