This feature is a result of a CSSWG resolution: https://github.com/w3c/csswg-drafts/issues/8407#issuecomment-1440466558 content-visibility: auto is a property that can be used to optimize rendering of off-screen content. However, when rendering is optimized it also means that the size of the element cannot be determined using the descendant information. This is done with size containment. As a result, contain-intrinsic-size was added to help with this. When content-visibility: auto skips contents, contain-intrinsic-size determines its size (roughly as if it had a single child of specified size). contain-intrinsic-size also has an option to add an "auto" keyword which means "if the element has been previously rendered, then use that size; if not, use the specified size". This helps with layout stability by ensuring that elements that come into the viewport and then leave remain the same size as before. This feature tracks forcing contain-intrinsic-size: auto if content-visibility's value is auto.