Ex post facto
I looked into this for some other reason, not long ago, and discovered that ex post facto law is considered a Very Bad Thing in the States (so only very occasionally allowed/tolerated), but this does not seem to be the case in the UK, where any number of recent major examples can be found in a fairly cursory internet search. I found that quite surprising, and pretty disappointing, too. pxd
Biting the hand that feeds IT
