In plain language
Everything must still work with text enlarged to 200% — nothing cut off, overlapping, or lost.
Who it affects
Low-vision people who enlarge text instead of using a screen reader.
How to check
Set browser zoom / text size to 200% and walk key pages: all text readable, all controls reachable, nothing clipped. Worked example — A job board's application form: set zoom to 200% and check any auto-truncating text (ellipsis): if JS measures pixel width and cuts content that was previously visible, it fails.
Common misconception
Responsive design is not the same as resizable text. A layout can adapt to screen width and still break completely when someone just increases their browser's text size to 200%. Real example: on a university's online course catalog, when text is enlarged to 200%, some text or controls get cut off, overlap, or disappear — content is lost for users who need bigger text.