I am getting into HTML 5 lately and a result of some investigations and querying the web in order to find great helpers, tools and open source frameworks, I bumped into the Modernizr.

This is a great open-source JavaScript library that helps you build the next generation of HTML5 and CSS3-powered websites.

The Modernizr (in simple words), helps you to find out which elements or features are being supported by each major browser.

Some of the features and behavior according the official website:

Modernizr aims to bring an end to the UA sniffing practice. Using feature detection is a more reliable mechanic to establish what you can and cannot do in the current browser, and Modernizr makes it convenient for you in a variety of ways:

1. It tests for over 40 next-generation features, all in a matter of milliseconds
2. It creates a JavaScript object (named Modernizr) that contains the results of these tests as boolean properties
3. It adds classes to the html element that explain precisely what features are and are not natively supported
4. It provides a script loader so you can pull in polyfills to backfill functionality in old browsers.