I have since learned that people like that it's disclosed if a question is cross-posted here and at SO, so apologies that I didn't do this - I know for future questions.

Thanks for following up here and for your apologies, which I accept on behalf of all of us. In case it isn't obvious, this is not just a PerlMonksism nor an SO-ism. Anytime you ask the same question in multiple places on the web it is only polite to inform the total strangers whom you are asking to provide you with expert advice for free that the question has been asked elsewhere too - and always include the links. There is rarely any point in someone answering the question if it has already been answered several times over elsewhere.