This gist was writen in 2012 and it was solving specific problem in Rails & SimpleForm. Some fellow developers were pointing out this may be out dated concept. That's why I advise everyone to read comment section bellow to have a full grasp of alternative solutions
other sources that may be helpful to understand why this may not be best idea:
Works great for me and seems robust: https://gist.github.com/jameslafa/337e6290115479c2e7e707a8978b7f5a