A lot of programmers believe they can parse HTML at all.
Go read the official W3C parser algorithm, I'll wait. First thing you'll notice is that there is no formal grammar - the spec is of the actual parser state machine. Then you notice each past-and-present HTML version has its own parser algorithm spec, and there is no official documentation on the differences between them, never mind rationale. Then you realize that HTML5 is now a "living spec", so the parser algorithm at that link occasionally changes, and past versions and changelogs are deliberately not published...
HTML is a parseable format like PHP is a programming language. There is no spec, there is only whatever bugs and quirks a particular browser version happens to contain.
(Oh, you thought browsers actually follow any of those published W3C specs? HAHAHAHAHA sob.)
HTML is indeed a turd of a standard.
There are some long lists of false beliefs that programmers hold. isn't because programmers are especially likely to be more wrong than anyone else, it's just that programming offers a better opportunity than most people get to find out how incomplete their model of the world is.
I'm posting about this here, not just because this information has a decent chance of being both entertaining and useful, but because LWers try to figure things out from relatively simple principles-- who knows what simplifying assumptions might be tripping us up?
The classic (and I think the first) was about names. There have been a few more lists created since then.
Time. And time zones. Crowd-sourced time errors.
Addresses. Possibly more about addresses. I haven't compared the lists.
Gender. This is so short I assume it's seriously incomplete.
Networks. Weirdly, there is no list of falsehoods programmers believe about html (or at least a fast search didn't turn anything up). Don't trust the words in the url.
Distributed computing Build systems.
Poem about character conversion.
I got started on the subject because of this about testing your code, which was posted by Andrew Ducker.