Render integrity is the degree to which a page's meaningful content is present in the delivered HTML without JavaScript execution. It matters because several AI crawlers do not execute JavaScript, so client-side content may be invisible to them entirely.
Test by disabling JavaScript and reloading the page.
Accordion and tab content is the most common casualty — collapsed is fine, injected on click is not.
This is a binary failure, not a degradation: the content either exists for retrieval or it does not.