[Twisted-web] How do I add a doctype using stan?

[Michael M]

Okay, I have searched but have not found an answer and I am sure it is
obvious. I am using nevow tags and want to have the doctype so that
validation works. I am not using xmlfile or xmlstr.

I tried to do the following.
docFactory = stan.loaders(
    tags.xml('DOCTYPE etc etc'),
        tags.html[
            tags.head[tags.title['Help']],
            tags.body['How do I add a doctype']
    ]
)

and of course it failed.

Any help appreciated.

Thanks
Michael