`position: absolute`

[chearon]

I'm almost done with this, but currently, containing blocks are assigned in the layout function (like layoutBlockBox) which are called as the tree is descended for layout. Because inline layout (createLineboxes) is called before descendants are laid out, an absolutely positioned inline that doesn't have a left/right will need to be positioned in createLineboxes according to what its position would be if it was not absolute. To do that, it needs to be laid out to get its size, but that's not possible if it has no containing block. So the current blocker is to assign containing blocks during box tree creation rather than as a part of the layout step.