doing something during build-time or at the beginning of run-time is equivalent time-wise

True, but the cost is moved to build-time and users are not bearing it :-) Suppose it takes you 0.50s to assemble a giant regex from smaller bits taken from a bunch of submodules. While the assembled regex literal only takes 0.01s for Perl to parse. Your module users will only take the 0.01s hit at startup time and not 0.50s.

if the stringification compiled regex doesn't suit your needs, why don't you dump the pattern before compilation

Yes, in this case I actually can, because I'm assembling the regex from strings. So before I turn it into a Regexp object, I can print the string first. My particular problem is solved. Thanks! :) But suppose I already have a regexp object? How do I stringify it under 5.14+ so it is compatible with 5.10 & 5.12?