Edit in JSFiddle

/** @jsx React.DOM */
var Hello = React.createClass({
  render: function() {
    return <div>{'Hello ' + this.props.name}</div>;
  }
});

xreact.register('x-hello', Hello);

<script src="http://fb.me/react-js-fiddle-integration.js"></script>

<!-- This HTML tag is going to be rendered with React -->
<x-hello name="World"></x-hello>