Do you want to know how the CSS WG works? Fantasai has written about:csswg, An Inside View of the CSS Working Group at W3C.
visibility: collapsestays in box tree, but has special layout: Do layout once normally, then collapse it to a strut of its line’s cross size and lay out again. (This keeps the cross-size stable if the flexbox has only one line.)
flex-basisfor sizing flex items, even inflexible ones.
autocomputes to the computed
height(as appropriate); on elements that are not flex items, it always computes to
autokeyword as the initial value of
min-height. On CSS2.1 display types it computes to zero; on flex items it is treated as
break-before/after: alwaystriggers a flex-line break, and all values that trigger fragmentation on an item in a row flexbox get propagated to the flex line.