http://www.perlmonks.org?node_id=814043


in reply to Re^3: Alternative to bytes::length()
in thread Alternative to bytes::length()

Looks like you found the caching mechanism. From perlguts:
w PERL_MAGIC_utf8 vtbl_utf8 UTF-8 length+offset cac +he

As for keeping bytes... meh, my attachment to the bytes pragma extended only to that use case, as the efficiency of CORE::length() with SVf_UTF8 scalars is a bummer. I'm not even going to bother posting to p5p now that my concern has been addressed another way.