If you're looking to test your HTML knowledge (and who isn't?), take a trip to the justsayhi website. How many elements can you name in five minutes?
As an aside, the JavaScript built into the test is simple but perfect -- an idea carried out well.
I work with an awesome cast of developers at Mozilla, and one of them in Daniel Buchner. Daniel's shared with me an awesome strategy for detecting when nodes have been injected into a parent node without using the deprecated DOM Events API.
I recently posted an awesome (if I may say so myself) CSS3 / MooTools tutorials called Create a Photo Stack Effect with Pure CSS Animations or MooTools. The post presented two ways, a pure CSS method or MooTools-powered class, to duplicate Google+'s elegant photo stack...
Aaron Newton made a great request to me last week: why not make my MooTools Documentation Bookmarklet function more like the New York Time's text selection widget. NYT's text selection widget listens for text selection and presents the user with a "search" icon...
Counters. They were a staple of the Geocities / early web scene that many of us "older" developers grew up with; a feature then, the butt of web jokes now. CSS has implemented its own type of counter, one more sane and straight-forward than the ole...
I make only 25 (the shame is over me :-D). I don’t know or remenber the existence of BDO, COLGROUP, ISINDEX, KBD, OPTGROUP, Q, SAMP, TT and VAR. The others i have a simple mind blank.