Hitch is a thin layer that sits in the browser and provides an "opt-in" extension model which allows you to use (or even define) additional selectors or html capabilities which are not currently a part of a standard. The hitch engine essentially turns uses selector hitches in your CSS into standard CSS which includes a hashed class name in place of your use and gives it back to CSS - it then simply manages the toggling on and off of those class names. The same underlying ideas are used internally to create a hitch mechanism for html components.