Thanks for participating so much here, I just came back from a quick trip to denmark, hence no answers until now.
Nico, without a link to your example we cannot help you, the examples work here, seems you added something wrong. I will set up a live site with some of the changes and fixes shown here, as I cannot reach the ALA hosted site :-)
As to some of the “simple” solutions posted here: There are oh so many different ways to reach this same effect, but I consider neither custom attributes nor inline event calls a good solution.
Custom attributes just add to more problems for inexperienced (x)HTML scripters. Let’s face it, in the world of generated code by blind editors it is hard enough to find clean code in big projects, a lot of developers don’t even bother scripting the current HTML correctly, when it works in forgivable browsers. Why add a non-standard attribute when ID and class do fine?
For all the people adding links here: Please make sure they work, and tell a bit about them, the multiple class one for example was rather useless, a link to the w3c standards would have made more sense. Please keep it on topic. Same goes for IE vs. other browsers, this is pure evangelism and not for here.