What is the :unique attribute for package variables?

[princepawn]

Yes, today is my day for going through all the perldelta docs and learning all sorts of new things. Well anyway I was reading perl591delta and I read this:

The :unique attribute is only meaningful for globals

Now applying :unique to lexical variables and to subroutines will result in a compilation error.

But a search for unique attribute yields no information.

What exactly is this attribute and how does it work? And where could I have found docs on it?

[princepawn]

Yes, and continuing on my delta safari, I see

:unique The :unique attribute has been made a no-op, since its current implementation was fundamentally flawed and not threadsafe.

[ForgotPasswordAgain]

perldoc -f our

(found by googling: perl unique attribute globals)