AngularJS directives are HTML attributes with an ng prefix. You can use data-ng-, instead of ng-, if you want to make your page HTML5 valid.
<div data-ng-app="" data-ng-init="firstName='John'">
<p>The name is <span data-ng-bind="firstName"></span></p>
</div>
<div data-ng-app="" data-ng-init="firstName='John'">
<p>The name is <span data-ng-bind="firstName"></span></p>
</div>