Adding on to this, while this article is fast approaching 20 years old, it gets into the quagmire that is web standards and how ~10 (now ~30) years of untrained amateurs (and/or professionals) doing their own interpretations of what the web standards mean--plus another decade or so before that in which there were no standards--has led to a situation of browsers needing to gracefully handle millions of contradictory instructions coming from different authors' web sites.

• Martian Headsets - Joel on Software

Here's a bonus: the W3C standards page. Try scrolling down it.