A modal is a form
I deleted a focus trap last October and was extremely pleased with myself, then read the dialog element's documentation properly and found the one method call that had been doing that job, and 4 others, since 2022.
Scroll wheels and zip codes
A customer was charged for 40 of something they had ordered 4 of, and the mechanism turned out to be a browser behavior sitting inside the one input type everybody reaches for.
Four sentences somebody could check
A client asked what progressive enhancement meant in practice and the 4 of us on the call produced about 90 seconds of gesturing, not one word of which anybody could have written down.
details and summary
An accordion with keyboard support, correct announcement and no JavaScript at all, which most of us reimplemented by hand for about a decade before noticing.
Outlook renders with Word
A client asked whether their newsletter could look like their new site, which is a completely fair question, and answering it honestly meant explaining that the biggest email client in the working world lays out HTML with a word processor.
fieldset and legend
A group of radio buttons has a question attached to it, and the question needs to be in the markup rather than in a heading that happens to sit nearby.
content: "\00a0"
Why the most-used string in my stylesheets is an invisible one, how CSS escapes will silently eat the character after them, and the parts of the content property that aren't strings at all.
optgroup
A select with 40 options in it is nearly always a select that wanted three or four labeled groups, and the element for that has been sitting in HTML the entire time.
The 400 KB hero
Every conversation about page weight goes straight to minification. Meanwhile there is a 2 MB image on the page that nobody has opened since Photoshop.
abbr and the title attribute
The abbreviation element is one of about four places in HTML where the title attribute is the actual content rather than a decoration, and it is still unreachable for anybody not holding a mouse.