Whitespace and control characters should not be permitted in tokens
As of Ruby 2.5.1p57, it appears that all valid Unicode code-points above 128 are permitted in tokens. This includes whitespace and control characters.
This was demonstrated here: https://gist.github.com/qrohlf/7045823
I have attached the raw download from the above gist.
The issue has been discussed on StackOverflow: https://stackoverflow.com/q/34455427/1858225
I would say this is arguably a bug, but I am marking this ticket as a "feature" since the current behavior could be considered by-design.