After checking perldelta for 5.005_3 and Elements of Programming with Perl, I have to conclude that lookbehind assertions were introduced in 5.005. Lookaheads were around before that, though.

As to why perlre for 5.004 shows that -- your guess is as good as mine.

In reply to Re: Lookbehinds not recognized? by chromatic
in thread Lookbehinds not recognized? by reptile

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