Right now we have two properties named margin-top-collapse and margin-after-collapse. They are proprietary and only used by Safari RSS.
I am adding margin-before-collapse and margin-after-collapse and just aliasing the old properties to the new ones. This way we have some names that are directionally independent.
Note that these properties aren't like other directional properties. They are about what to do with the before side and after side of your block's margins when collapsing with adjacent blocks. The meaning of before/after depend on the block-flow directionality of the containing block.
Created attachment 69100 [details]
Fixed in r68561.