This feature extends the existing contain-intrinsic-size syntax: none | <length> | auto && <length> to also include auto && none: none | <length> | auto && <length> | auto && none The reason for this change is the CSSWG resolution (https://github.com/w3c/csswg-drafts/issues/8407#issuecomment-1440466558) to add an interaction between content-visibility: auto and contain-intrinsic-size. Specifically, that the former adds an "auto" keyword to the latter. For this to work, the resolution includes a note to extend contain-intrinsic-size syntax for "auto" to work with all existing keywords, including "none".