> Serily: why would you unhesitatingly prefer 'P' to 'p'?

My name is Serhiy. :)

'P' has the advantage that you can safely backward-compatibly remove the
restriction by replacing 'P' on 'p'. :)

> I also found some funny in-between cases.

This is historical legacy, some still use 1/0 instead True/False. In the
end, bool subclasses int. But we have no middlecase for latin 'P'.