Hi Antoine,
you we're doing it right, the auto-complete reads the words from the SDF file...
You did edit the file but you must restart Twistpad in order for it to refresh the HTML keywords.
Yes you can add the HTML5 specification tags on keyword7 and beyond.
For the CSS3 tags you should create a new header group, similar to the [kCSSKeys] group
Let me know if you need further info.
Thanks,
André Santos Carthago Software Support
http://www.carthagosoft.net