Something that keeps coming up is the behavior of grid items set to position: fixed.

My understanding of this is that an item set to position: fixed should behave in the same way as one set to position: absolute, so that would correspond to 10.2 With a Grid Container as parent which seems to be what the 2 implementations are doing. CodePen example

However this is a bit confusing if you haven't made that connection. So if this is correct behavior perhaps a note could be added to clarify that this is how position fixed items will behave. It also seems as if having a fixed item be contained within it's track might be useful - but perhaps that is a different issue.