> Just to distinguish from Object layers, this ordering should probably be called Z-ordering or similar.

A hyphenated name is impossible, though. I've considered simply "z" because that's what it is (well, apart from the other z that is called Parallaxity). But z is an awfully short name.

> That's why I am doubting if binding game mechanics on to certain ranges of z-orders is such a wise idea.

Well, we need something. Using the layer isn't in of itself worse than using x and y. It's only that various other stuff that had nothing to do with the position was also triggered off those categories that created this mess. If we refrain from doing that and only use the layer for stuff where the position of the object should matter, we should be fine. That's one reason I mentioned explosions: It just makes sense that explosions affect a certain area. On the other hand, it certainly doesn't make sense to make gravity depend on the position of an object. At least in the small confines of a Clonk landscape ;-)

> However, I don't have an overview of what all this special-category-behaviour consists of so this suggestion just comes from what the data I have.

The problem is, the list of stuff that depends on the category defies summaries. I'd encourage you to do a search in the engine for C4D_StaticBack and the other categories and take a look at a few results that check whether a Category has that flag. There are often comments or self-documenting function names in the vicinity explaining the reason for the check: "staticback must not have speed", "Must be static back: this excludes trees that have already been chopped", "IsMoveableBySolidMask", "living takes additional dmg from blasts", etc. Compiling a complete picture would be a waste of time, though :-)

And yes, I don't plan on pushing this before the release.