So here we’re collecting all the shims, fallbacks, and polyfills in order to implant html5 functionality in browsers that don’t natively support them.

The general idea is that: we, as developers, should be able to develop with the HTML5 apis, and scripts can create the methods and objects that should exist. Developing in this future-proof way means as users upgrade, your code doesn’t have to change but users will move to the better, native experience cleanly.