The PPIx-Regexp package provides a PPI-like parse of Perl regular expressions. Part of its functionality includes reporting on the versions of Perl under which a given regular expression or its elements are valid. Up to this point the version fumctionality has been fairly simple: method perl_version_introduced() returns the version of Perl that introduced the element, and perl_version_removed() returns the version under which it was removed, or /users/tom_wyant/2017/07/index.html