What changes?
When order affects meaning, WCAG requires a correct sequence to be programmatically determinable. Visual placement, document structure, and keyboard navigation should tell the same coherent story.
Use it in your work
Keep a task introduction before its instructions and action when columns stack.
A common mistake
Reordering content visually while leaving a confusing document order.
Context matters
There may be multiple correct orders for independent items; preserve order where meaning depends on it.