HTML5 is the fifth generation of the hypertext markup language standard that is at the core of the World Wide Web. HTML5 combines and improves upon the features of HTML4 (standardized in 1997 by the W3C), XHTML (a “reformulation” of HTML4 and XML), and the DOM Level 2 HTML specifications. And as of this writing, it is still considered under development even as XHTML2 is in the works.

The mission (perhaps the spirit) of HTML5 is to serve as a unifying multimedia language for both humans and machines.

The Expressive Web is an HTML5 and CSS3 resource from Adobe that showcases some of the newest and coolest features in use today. Features pushed to the bleeding edge on sites like The Hunger Games’ The Capitol Tour and Project Prometheus Training Center. The fact that this site comes from Adobe (the people who bring you Flash), reinforces the company’s commitment to embracing web standards.

Both sites mentioned above were a little choppy under Safari and Chrome on my iMac running Lion but both sites also strongly urged the use of Internet Explorer 9 for the best performance (alas, not an option for Mac users). This is due largely to IE9′s support of Canvas which these sites make heavy use of (probably). Despite reports to the contrary, the interactivity is not quite on par with Flash but it is getting impressively close.

Want to keep abreast of the latest in HTML5 news? I recommend following Mashable’s HTML5 channel. Of course, developers should also check out HTML5 Rocks and  HTML5 Boilerplate (to name two).

At Mashable’s Christine Erickson’s behest, I installed Blackline app on my iPad, a new satirical magazine that was done entirely in HTML5 (I think entirely, maybe it’s mostly). Besides the edgy wit found throughout (which reminded me of National Lampoon when National Lampoon was funny), the Maya Angelou’s Ice-Box magnetic poetry was a hoot and a perfect example of interactive HTML5 (be sure to listen to the intro by Maya herself).