Oxygen XHTML Editor

Oxygen comes with XHTML catalog and document templates so that you can start creating XHTML documents right away. Also a ready to use sample is provided in the samples project giving you a head start when working with XHTML. It allows a very flexible document creation management through document templates. You can easily create new XHTML document templates from the editor content and you can publish your templates to share them with other users. HTML documents can be converted during load (imported) to XML allowing you to benefit from the XML support like XPath queries and XSL transformations for instance. During this process you can also associate an XHTML DTD with the new converted document (either the strict or the transitional XHTML DTD) so the converted document is ready to be validated against the specified DTD.

http://www.oxygenxml.com/xhtml_editor.html