None of the current browsers—so far as I know—recognize most or any of the new elements, such as <header>, <nav>, <section>, <footer> etc. They just tolerate them, treating them as unknown, inline elements. And no browser understands the document structure of HTML5, which is a big part of what it's all about. Just saying.
I guess I was referring to HTML5 in the umbrella-term sense of the word (encompassing CSS3 and jscript)
That's a common problem with the term HTML5. It's become a kind of mythological wonder language that can do anything—when in truth it's just HTML with some new elements, and CSS and JS are separate languages that HTML(x) still relies on do do much.