The following regexp does not parse/compile: /\A((x)|(y))(?(2)y|x)\z/

Here's the error it produces:

[] ~/projects/jruby $ jruby -c test/mri/ruby/test_regexp.rb 
SyntaxError in (RegexpError) undefined group option: /\A((x)|(y))(?(2)y|x)\z/

As you can see this prevents test_regexp.rb from running. It has not been running for over a year (excluded from test:mri run) and we should really fix this for 9k final.