This module works around two historical bugs in Perl's handling of the %^H
(lexical hints) variable. One bug causes lexical state in one file to leak
into another that is required/used from it. This bug, [perl #68590], was
present from Perl 5.6 up to Perl 5.10, fixed in Perl 5.11.0. The second bug
causes lexical state (normally a blank %^H once the first bug is fixed) to
leak outwards from utf8.pm, if it is automatically loaded during Unicode
regular expression matching, into whatever source is compiling at the time
of the regexp match. This bug, [perl #73174], was present from Perl 5.8.7
up to Perl 5.11.5, fixed in Perl 5.12.0.