Expand description
External $ref resolution.
The parser’s default parse_str path uses NoExternalResolver,
which rejects every external ref with parser/E-EXTERNAL-REF. The
file-based parse_path entry installs a
FileResolver that loads adjacent JSON documents (caching by
canonical path) and refuses any path that escapes the input file’s
parent directory.
The schema walker calls Resolver::load when it encounters a $ref
whose path part is non-empty; it then walks the target component just
like a local one, prefixed with the external document’s stem so IDs
stay globally unique inside the type pool.