A nice explanation for someone who has not looked into Arc (me). [0-9a-zA-Z]{10} is what, 840 quadrillion combinations? Just out of curiosity, what happens if

A nice explanation for someone who has not looked into Arc (me). [0-9a-zA-Z]{10} is what, 840 quadrillion combinations? Just out of curiosity, what happens if we get a 'fnid' collision? I expect to be serving a few hundred trillion pages in a couple of years time :-p.