SchemaLocation

Where one subschema lives: the document that carries it, and a JSON Pointer into that document.

This pairs with an instance location to make a cycle detectable. The reference graph a catalog describes is genuinely cyclic — a function's arguments are dynamic values, a dynamic value may be a function call, and a function call resolves back to the catalog's own functions — so a traversal that tracked only the instance would revisit the same subschema forever on a value that never shrinks.