It's looking to me like perl5's embedded pattern modifiers don't work
when used with raku's :P5 compatibility modifier...
printf "%-25s", "Trying raku style: ";
if "this" ~~ m/ ^ <[a..z]> / { say "good"; } else { say "ng"; }
printf "%-25s", "Trying :P5 without (?^x: ";
if "this" ~~ m:P5/^[a-z]/ { say "good"; } else { say "ng"; }
printf "%-25s", "Trying :P5 with (?^x: ";
if "this" ~~ m:P5/(?^x: ^ [a-z] )/ { say "good"; } else { say "ng"; }
printf "%-25s", "Trying :P5 with (?^i: ";
if "this" ~~ m:P5/(?^i:^[a-z])/ { say "good"; } else { say "ng"; }
# OUTPUT:
# Trying raku style: good
# Trying :P5 without (?^x: good
# Trying :P5 with (?^x: ng
# Trying :P5 with (?^i: ng
