And, in passing, group upper- and lower-case switches properly.
For: RT 133044. Thanks to contributor KES.
X<PERL5OPT>
Command-line options (switches). Switches in this variable are treated
-as if they were on every Perl command line. Only the B<-[CDIMUdmtwW]>
+as if they were on every Perl command line. Only the B<-[CDIMTUWdmtw]>
switches are allowed. When running taint checks (either because the
program was running setuid or setgid, or because the B<-T> or B<-t>
switch was used), this variable is ignored. If PERL5OPT begins with