Invalid state

A red border is a picture of a problem, not a report of one. aria-invalid="true" is the report: it makes the field itself say “this value was rejected”, so the state travels with the control into the accessibility tree instead of living only in the pixels. Screen readers speak it as part of the field, which is why a person tabbing back into a form hears that the field is wrong at the moment they arrive on it, rather than having to go hunting for red text. The attribute also takes grammar and spelling, both for a narrower claim about a particular span of text, and false, which is the default and rarely worth writing.

The mark on its own is only half a sentence. It says something is wrong and not what, so it has to be paired with a pointer to the explanation: aria-describedby naming the element that holds the message, which every screen reader in use supports, or aria-errormessage, which is the purpose-built version and is still unevenly implemented, so the pragmatic build uses aria-describedby and adds aria-errormessage alongside it. Either way, the message element has to be present and visible, since a description pointing at a hidden node is announced as nothing. What that message should say belongs to error message.

Timing is where most implementations go wrong. Flag the field after validation has actually run, which usually means on submit or on blur, and never on every keystroke: someone typing their email address is briefly holding an invalid value on the way to a valid one, and a screen reader announcing “invalid entry” after each letter makes the form unusable. Clear the flag the moment the value passes, so the state never outlives the problem. The whole timing question, including how early is too early, is the subject of inline validation, and the wider requirement to tell people what went wrong and how to fix it is error identification.

The failure this term exists to name is the styled-only field: red border, red text underneath, nothing in the accessibility tree. It announces exactly like a field that is fine, so the only people who learn there is a problem are the ones who can see the colour, which is the same population the red already served. It is a one-attribute fix that no visual review will ever catch, because on screen the broken build and the correct one are identical.