What does this regexp do?

< ^ > P N |<>|^_>< --- | ~ ...Help

I can't figure out what this does:
 >> "1\n2\n3\n"[ /.\Z?/ ]
=> ""

I would expect it to output "1", just as:
 >> "1\n2\n3\n"[ /.(\Z)?/ ]
=> "1"

Is this a bug?

--
Daniel