Why a Vague Error Banner Fails the Understandable Principle
A signup form rejects a submission and shows only a red banner reading "Error" at the top of the page — no indication of which field failed or what to change to fix it.
Which WCAG POUR principle does this failure fall under?
The correct answer is "Understandable."
Understandable requires that information and interface operation be clear to the user — SC 3.3.1/3.3.3 (Error Identification and Suggestion) specifically require identifying which field failed and suggesting a fix, not just flagging that something went wrong. A generic "Error" banner is unclear to every user, and actively blocking for someone with a cognitive disability.
Perceivable is satisfied here — the banner is visible and readable. Operable isn't the issue since nothing prevents interacting with the form. Robust concerns consistent assistive-tech interpretation, not the clarity of the message's content.
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