Dept wants us to add half a dozen mp3 files to one of the pages on their site. I thought I'd take the chance to see what would be involved in updating the page from 2002-era html 1.0 transitional to html5 so I could include an audio element.
There were a couple of upper-case / lower-case issues with attribute values, and a number of no-longer-supported attributes for table elements (e.g. border="0", cellpadding="0", cellspacing="0"). I eventually got the page to validate as HTML5, but have a couple of stubborn table cell borders that show up when I don't want them to.
The navigation structure is generated by javascript and included on each page, so when I made the modifications to ensure validation against html5, I started to get some unwanted artefacts on all the rest of the pages on the site.
I might be able to thrash out the gui issues so that the shared elements work in both xhtml-1 and html5, but I'm not sure it's worth the bother for this page on this site.
I do wonder what kind of support the cascade pages have for html5, as people will want to include media elements (and do other things afforded by html5).