> When did it come about?

I don't know, but the OP wants $vars which can be used inside Perl code. (which is also documented in multiple ways)

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

update

see Re^2: Refer by relative way to regex group (eg. the last one)

In reply to Re^3: Refer by relative way to regex group (eg. the last one) by LanX
in thread Refer by relative way to regex group (eg. the last one) by Anonymous Monk

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