@deeky666 I've [raised the same question](https://github.com/doctrine/doctrine2/pull/949#issuecomment-40766339) in my other PR, but still haven't received any comments in this regard.

TBH I still can't think about any use case where this would be useful. And doing that would complicate the underlying code: what happens if you do:

    $transaction1 = $em->createTransaction();
    $transaction2 = $em->createTransaction();
    
    $transaction2->begin();
    $transaction1->begin();

They would now not follow the order of the transaction stack in the TransactionManager, and that could be a pain to handle?