Modernizr tests which native CSS3 and HTML5 features are available in
the current UA and makes the results available to you in two ways:
as properties on a global Modernizr object, and as classes on the
<html> element. This information allows you to progressively enhance
your pages with a granular level of control over the experience.
Modernizr has an optional (not included) conditional resource loader called Modernizr.load(), based on Yepnope.js (yepnopejs.com). To get a build that includes Modernizr.load(), as well as choosing which tests to include, go to www.modernizr.com/download/
Modernizr is dual-licensed under the BSD and MIT licenses.
Try it out:
Run the library: http://modernizr.github.com/Modernizr/output.html
Run the test suite: http://modernizr.github.com/Modernizr/test/