Further to this (not that this thread isn't long dead), in Terje Kristensen's latest minigolf competition he came up with this:

-n $;[map{/./,/[^$&-T]/g}/(?=(.*))/g].=$_}{print@
[download]

Which does funny non zero width things for (?=)

perl -le 'print for "foo bar"=~/(?=(.*))/g'
foo bar
oo bar
o bar
 bar
bar
ar
r
[download]

I had no idea this would happen, anyway.

Jasper