Extending the html schema

Question

I'm trying to create a templating engine not too synactically far from ASP.net WebForms. I want the markup to look like this:

<ext:Templates xmlns:ext="http://www.myschema.com/" xmlns="http://www.w3.org/1999/xhtml"&gt;
    <ext:Template name="Template1">
        <div id="someid" style="display:none" ext:extendedAttr="someValue">
            <ext:DivProperty name="X"/>
            Some text
            <span>... more text</span>
        </div>
    </ext:Template>
</ext:Templates>

In effect, I want to extend all html elements to allow attributes and elements of any type that belongs to the http://www.myschema.com namespace. Is this possible without modifying the HTML xsd?