And w3schools is provided as a reference :|
Its layout is reasonable, and it seems to have a fairly comprehensive coverage of the topic. Its not overwhelming like w3.org. I can find what I want to know with relative ease (unlike w3.org)
I have seen a couple of articles pointing out that their implementation details are bad, but I don't think I have ever gone on there with the intention of clicking "view source"
w3.org is the W3C, the actual organisation that publishes the CSS and XML specs (and the versioned snapshots of the HTML spec).