http://www.anthonycalzadilla.com/2010/08/html5-section-aside-header-nav-footer-elements-not-as-obvious-as-they-sound/

The new HTML5 SECTION element can be somewhat confusing. If you’ve been building HTML documents before HTML5, chances are you are already using the DIV element to create structural divisions within your pages and then style the pages with them. So it might seem like a natural thing to simply replace your existing DIV elements ...

http://dev.w3.org/html5/alt-techniques/#tree A simple alt text decision tree