Why does it evaluate to zero
It does not ;-) add a print "\n"; after that and you'll see.

Meaning:

print //;   # pattern-match an empty string. result: 1
print \\//; # ref to ref to variable holding 1 (1)
print \\\//; # ref to ref to ref to variable holding 1 (2)
print \\///\\\//; # print (1) / (2)
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Since references return memory addresses when accessed as numbers, the last line will result in some value close to 1, just a little smaller (this is because (1) is allocated before (2)).

Anyway, that's my guess. Anyone care to point my mistakes?

-mk