Definition and Usage
The <video> tag defines video, such as a movie clip or other video streams.
XHTML2 has some very good ideas that I hope can become part of the web. However, it’s unrealistic to think that all web authors will switch to an XML-based syntax which demands that browsers stop processing the document on the first error. XML’s draconian policy was an attempt to clean up the web. This was done around 1996 when lots of invalid content entered the web. CSS took a different approach: instead of demanding that content isn’t processed, we defined rules for how to handle the undefined. It’s called “forward-compatible parsing” and means we can add new constructs without breaking the old.
So, I don’t think XHTML is a realistic option for the masses. HTML 5 is it.