Convert HTML to OpenXML format using XSLT

I work on a PHP project, the client can create Microsoft Office models, and then use them to generate .docx documents.

In these models, the client can specify some free text areas, and at the generation of the document, a wysiwyg editor is provided to fill the areas.

I'm searching a XSLT template to transform HTML code from the editor to OpenXML format. Is there a ressource for that or a tool ?

Thanks.