In plain language
Controls and meaningful graphics (input borders, icons, focus outlines, chart lines) need 3:1 contrast against what's next to them.
Who it affects
Low-vision and color-blind people who need to perceive controls and meaningful graphics.
How to check
Use a contrast checker on input borders, checkboxes, icons, focus outlines, toggles, chart elements — including hover/checked/selected states. Worked example — A crowdfunding platform's campaign page: measure the visual marker for a selected state (tab underline, active card border) against its background: 3:1 minimum.
Common misconception
People assume 1.4.3's text contrast rules cover everything. This is a separate rule for non-text elements, borders, icons, focus outlines, that has its own, lower 3:1 threshold. Real example: on a food-delivery app's order-tracking screen, cSS removes or hides the focus outline (outline:none / border removal) with no replacement — keyboard users can't see where they are on the page.