This JRuby spec https://github.com/jruby/jruby/blob/master/spec/ruby/language/regexp/modifiers_spec.rb#L103-L108 is tagged https://github.com/jruby/jruby/blob/master/spec/tags/ruby/language/regexp/modifiers_tags.txt#L1 because Joni doesn't yet have support for ASCII/Unicode modifiers. Onigmo commit: https://github.com/k-takata/Onigmo/blob/master/regparse.c#L5170.