HTML elements in a DocBook file

Hello,

I have recently found that, as long as you declare the HTML namespace
in the root element, you can "embed" native HTML elements in your
DocBook files.

Looking at the docs shows me that most of the <html:form> related
elements are valid for the DocBook DTD. I would like to include a few
more HTML elements such as <html:title> and perhaps <html:meta> etc.

I know this is possible, because Mozilla renders this as expected -
but is this valid DocBook (as the elemtents are not defined) and if
not why?

Thanks,
Noah Slater

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"Creativity can be a social contribution, but only in so
far as society is free to use the results." - R. Stallman