The code is this repo is very old and is here to be read and learned from. It is not maintained. 🕶 - - - class Stuff class << self include HTMLDiff end # or extend HTMLDiff ? end Stuff.diff('a word is here', 'a nother word is there') # => 'a<ins class=\"diffins\"> nother</ins> word is <del class=\"diffmod\">here</del><ins class=\"diffmod\">there</ins>' Checkout the crappy specs for good examples.