Import

A package import specification. An import is one of two things, chosen by `mode`: a DEPENDENCY (the default) — schema this document needs to mean anything (the classes its `type`s name, the properties it uses and their ranges, the `subClassOf` chain), which is fetched with the document, is part of its closure, and must not form a cycle — or a LINK — a package this document merely addresses resources in (an object-property value naming an entity there), which is dereferenced on demand, never enters the closure, is exempt from the cycle rule, and resolves version-agnostically unless pinned with `=`. A reference to a resource is not a dependency on its package; any graph with mutual references (spouse and spouse, part and whole) is representable only because the two are distinct.