General Principles:

• HTML5 compliant: correctly and accurately implemented (HTML5) Markup-, JS- and DOM-APIs
• capability based loading: extremely lightweight in modern browsers
• cross-browser support: All A-Graded browsers including latest version of Opera are tested
• extendable: if we have not implemented a feature you want, you can easily implement it on your own

Implemented Features:

• HTML5 shiv and innerShiv solution including basic CSS-support
• canvas
• HTML5 form features including: constraint validation and form widgets (input[type="range"], input[type="date"], input[type="number"], output, input[list]/datalist)
• HTML5 audio/video/track implementation
• interactive elements: summary/details
• JSON (stringify and parse)
• localStorage/sessionStorage
• geolocation
• ECMAScript 5 / JavaScript 1.8.5 features

• Simply download Webshims Lib and put the js-webshim-folder in your project
• Include the JavaScript:

<script src="js/jquery.js"></script>
<script src="js/Modernizr-yepnope.js"></script> 
<script src="js-webshim/minified/polyfiller.js"></script> 

<script> 
	//load and implement all unsupported features 
	$.webshims.polyfill();
	
	//or only load a specific feature
	//$.webshims.polyfill('geolocation json-storage');
</script>

• Wait till everything has been loaded and then use it:

<script> 
	$(function(){
		//work with JSON and localStorage 
		var userData = JSON.parse(localStorage.getItem('userData')) || {visits: 0};
		$('#visits').html(userData.visits);
		//...
	});
</script>

More information and demos here.

The Webshims Lib core is licensed under the MIT-License. Note: Webshims Lib uses many great third party scripts.

If you have any questions, please feel free to ask them on the Using jQuery Plugins forum.

Please tag your questions with 'webshims' or 'polyfill'.

• improved rtmp handling for both Jaris and JW player
• fixed bug on iOS in conjunction with input[type=date]
• fixed creditcard validation
• allow placeholder for type=number
• show mediaelement fallback, if flash isn't installed and mediaelements aren't supported
• a lot of improvements to the free and open source swf media player Jaris (we will switch to Jaris by default with next release)

• add option to use alternative jarisplayer as mediaelement fallback
• fixed track[default] in IE10 (initial copying of track.mode)
• implement .prop-checked in browsers, which do not support the :checked selector
• implement .user-error selector
• limit track.kind property using addTextTrack to only known values

• implemented input[type="time"]
• allow dynamically changing label/kind/srclang of existing track elements
• added removeCue to texttrack API
• added screenreader-support for track[kind="descriptions"]
• improved change events for input[type=range] and spinbutton controls (input[type=number])

• added onaddtrack/onremovetrack events to TextTrackList interface
• datalist polyfill is now default for forms feature
• added swedish locale (thx to @leon)
• improved errorbubble style
• updated JW player