I’m started reading how to program HTML 5 by following Sitepoint’s book on the subject. I’ve created a very simple HTML file but when I open it in IE 9, it isn’t displaying as I’d expect it to. For example, the tag <details> & <summary> aren’t showing a collasped element.
I’m using Visual Studio 2010 and I created an ASP project so I thought this was the issue but even when I copy the text into a regular file with a .HTML extension, the page is rendered correctly.
See this page on HTML5 support in IE9 where it list what is supported and what isn’t. You’ll find that your experience matches up.
Basically, HTML5 is still in draft mode, and only has patchy support among most web browsers. Some provide near-full support, whereas others do not.
HTML5 is far too new to use for public web pages. Give it 5 years or so though, and web browsers should have caught up by then.