title: How are the attribute prefixes "x-" and "data-" used in AngularJS
body: <p>I'm new to Angular and trying to understand what the "x-" and "data-" prefixes mean. In the directives documentation (<a href="http://docs.angularjs.org/guide/directive">http://docs.angularjs.org/guide/directive</a>) it says that these prefixes will make the directive "HTML validator compliant". What exactly does this mean?</p>