Jens, Dave, I agree that auto-layout is a bit touchy. If it's any help, I think that under the hood it is solving a problem in "linear programming," https://en.wikipedia.org/wiki/Linear_programming .

BTW, frequently I wish for the boxes & glue (& penalties) layout model that Plass & Knuth famously used for typesetting (TeX and all that). I believe the default layout manager for NSTextView uses tha

Graham, I am picturing a radix trie with n-bit keys where n is 32 or 64—whichever suits your z-orders. Keys represent the z order. Each object is a leaf in the trie. In each object, store its z-order

[I'd sent this to cocoa-dev@..., but ISTR that list is deprecated. Resending here.] I am working on a document storage format that consists of logical zones that nest. You can think of the