[zackattack]

'z'++ is not 'aa'. 'z'++ is not even valid PHP. $z='z';$p=$z++; does nothing either.

it's only in the for-loop context.

[Nitramp]

Not really, after $p = $z++ $p is 'z', $z is 'aa', as you'd kind-of expect. But the difference between literals and expressions/variable references of course just adds icing to the cake of bizareness.

[rythie]

try...

<?php $z='z'; echo ++$z;

which produces 'aa'