[Bromskloss]

Couldn't you still use -1 to refer to the last grid line (or was it grid element)? Python does it, for example.

[kybradeck]

Yes, but that would mean the first gridline == 0 and the last gridline == -1, instead of the way the spec is written today, where the first gridline == 1 and the last gridline == -1. For me, consistency wins here.