R&R question

Someone asked me an interesting question about revise and resubmits the other day. If a philosopher, call them X, submits a paper to journal Y, and the editors return a revise & resubmit assessment, what obligations is X under. Obviously X doesn’t have to resubmit the paper to Y. But should X regard the paper as still under submission at Y? If so, X is obliged to either formally withdraw the paper from Y or not submit the paper elsewhere.

I think the answer is no, that once the editors have returned a submission, the paper is no longer under submission. X may resubmit the paper to that journal, but that would be a new submission. (As the wording ‘resubmission’ suggests.) So it’s OK to send the paper to a new journal without informing Y. But I can see a counter. At some journals (including, perhaps, one or two that I edit), R&R’s are such a crucial part of the editorial process, that one could regard them as moves in the process of considering a paper. In that case, the submission would still be active, and X would be obliged to not submit the paper elsewhere without formally withdrawing it from Y.

What do you think?