Hi vr,

my $regex = qr{(??{ join '|', map {quotemeta} qw/. | %/ })};
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Another excellent idea, thank you! I've updated my root node.

it's eval'ed "before parsing a regex", while s///e is not about it at all

Yes, you're right, it was misleading of me to write that qr//e would be "analogous to s///e", since in s///e it's the replacement part that gets evaled, not the regex.

Update: Your solution has the interesting feature that the code gets reevaluated every time:

use Test::More;

my @values = qw/abc def/;
my $re = qr{^(??{ join '|', map {quotemeta} @values })$}i;

like 'ABC', $re;
like 'DEF', $re;
unlike 'GHI', $re;

push @values, 'ghi';

like 'ABC', $re;
like 'DEF', $re;
like 'GHI', $re;

done_testing;
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Thanks,
-- Hauke D