As far as the latter goes, perlre specifies clearly that it's the same as that involved in capturing and using numbered vars.

That's only true if there are no other capture-less regexps in the program. Do you know where the OP intends to use your solution? When given two choices which are otherwise identical, one should pick the one that fails safe, the one that will cause no harm when the program is used in an unexpected manner.

Update: Added last sentence.

In reply to Re^4: Case conversion by ikegami
in thread Case conversion by anniyan

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