It is likely more use cases for this syntax will come up in the future (like the incomplete proposal to describe valid USE flag states with it), so explicitly referring to the valid contents in sentences like "any-of dependencies only make sense for dependencies and licenses" is unfortunate. It would be better to keep the description of any-of groups and the like more general and move extra restrictions to the place where they actually apply. If this is considered a good idea I will try to come up with a reasonably complete patch. (There are two reasons for this change: to allow extending the "depset" syntax in a future EAPI and to allow using this syntax in different places in a future EAPI).
AFAICS, the way it is currently makes it easiest to extend things without accidental consequences. any-of and all-of groups have entirely different meanings depending upon where they appear.
This whole thing's been reworded now.
