It doesn't turn out to be a big problem since you don't generally mix idioms in the same file. In a Rails app, it's pretty easy to figure out which files are evaluated by which DSL. If you're using HAML, anything in app/views with a .haml extension is HAML. Anything under /spec is Rspec. Capfile, Gemfile, and Rakefile are self explanatory. routes.rb uses the Rails routing DSL.