Looks like perlop need updating to warn of this qr/STRING/msixpodual, you should perlbut it :)

Also, this perldelta note is findable with perldeltas - every perl*delta in one file with each version properly linkable searching for "qr/" will eventually find "perldeltas.html#p5101-Other_incompatible_changes" :)

Searching for "/m" will after about a dozen "next" clicks land on "perldeltas.html#p5120-Errata" which also mentions this (see perl5120delta#Errata )

I also think its important to note there exists a warning/linticism for this :) Perl::Critic::Policy::RegularExpressions::RequireLineBoundaryMatching - Always use the /m modifier with regular expressions.

So next time, try to search the Perl::Critic rules, and perldeltas :) the really visible/common changes/caveats usually show up in these two places :)