HTML5 tag supported?

I couldn’t find it in the documentation, but from what I’ve seen so far it looks like the HTML5 video tag is only supported if the client computer is able to support it. I’ve been doing some testing on XP (because some people are dedicated), and I’m still getting a flash fallback on my video plugin.

For rendering HTML5, HTML Executable 4 uses the rendering engine of Internet Explorer. So to render HTML5, XP customers must have IE9 or higher. Otherwise, it won’t work.
In the incoming HTML Executable 5, we are adding Chromium-based engine, with the goal to support HTML5 and the video tag if possible.

That’s what I figured. Thank you for your help.