What the standard says
Instructions provided for understanding and operating content do not rely solely on sensory characteristics of components such as shape, color, size, visual location, orientation, or sound.
Why it matters
"Click the round button on the right" means nothing to someone who cannot see the layout or is using a 320px screen where nothing is on the right.
What a failure looks like
- fails"Fill in the fields marked in red."
- fails"See the box below" in content that reflows on mobile.
- fails"Press the arrow icon" with no accessible name on the arrow.
How to fix it
- doName the thing: "Fill in Email and Postcode", not "the fields marked in red".
- doAdd the visual cue as extra, never as the only cue.
How A11ySignal checks it
manual
No automated rule can judge this criterion, and we will not pretend otherwise. A clean scan does not mean 1.3.3 passes — it means nothing we can measure fails. This one needs a person.
What a tool cannot tell you
This one is entirely a reading exercise. No tool detects it.