Interesting new feature in HTML5 is the ability to define your own custom attributes[1] that will be valid HTML5 markup. In other words these attributes will pass an HTML5 validator.
This is useful for adding metadata to controls that can be manipulated by JS code. For example, instead of using an element's title attribute to add tooltip information, one can use data-tooltip="This is a tooltip". Should come in handy. Bob [1]: http://html5doctor.com/html5-custom-data-attributes/
