Blindness

Design considerations

• All content must be present in text or in a text equivalent, because screen readers can't read non-text content.
• All functionality must be available using only a keyboard, because while most blind users can physically move a mouse or trackpad, they can't see where the pointer is.
• Semantic HTML is key, because screen readers offer blind users the ability to navigate by headings, landmarks, and other semantic elements, and also uses those elements to describe what the user is focusing on.
• Custom controls must have the correct name, role, and value, and must change that value when appropriate, so that blind users can understand what is going on.
• Users must receive immediate feedback after all actions, because if the browser is silent, the user doesn't know if what they did had any effect.
• Videos must have audio descriptions if the current audio doesn't describe what's going on in the video -- anything that's purely visual content must be described.
• Touchscreens (primarily on mobile devices) use swipe actions to control the screen reader, so custom swipe actions generally won't work (or will break the screen reader). Similarly, all features require a click action to work.

Source: Deque University accessibility training.