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.
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.
I couldn't read it in the sun
I took my phone out to the front steps to look at a page I'd built, couldn't read a word of it, and then found that every pair of colors on it cleared the threshold with room to spare.
prefers-reduced-motion
An operating system setting that has been sitting there since 2013 telling you somebody gets motion sick, and the two-line stylesheet that is the whole of respecting it.
Six kinds of white
A client asked what it would take for their site to go dark along with their laptop, I said half a day, and then I searched the stylesheet for white and got 61 results.
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.
Alt text is writing
Every image on the site had an alt attribute, the checker reported zero errors, and not one of those attributes told anybody anything because filling in a field and writing a sentence turn out to be different jobs.
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.