YAML

YAML backend for the cfg protocol.

Load one or more YAML files and receive a Node.IMap[Id.Root] ready for decoding. Parsing is done by snakeyaml-engine with the YAML 1.2 core schema, so ~, null, Null and NULL are nulls, and << merge keys are resolved while composing.

==Merging== When multiple URLs are supplied they are overlaid in order — later files take precedence over earlier ones (last-wins). Mappings are merged recursively, key by key; scalars and sequences are replaced outright rather than concatenated. An empty argument list yields an empty root map. Unlike the HOCON backend there is no substitution step: a YAML file is taken exactly as written.

==Tags== Unlike the HOCON backend, this one reports tags. tag holds the tag as it was written in the source, already expanded through the tag handles in effect (!!int becomes tag:yaml.org,2002:int, a local !postgres stays !postgres). It is None whenever the tag was inferred by the resolver rather than written down, and also for the non-specific tag !, which says nothing about the type. Scalars are always carried as raw strings — a tag never converts a value, it only records what the author asked for, and acting on it is the decoder's business.

==Duplicate keys== A mapping that repeats a key keeps the last occurrence, matching the last-wins rule used for merging.

==Thread safety== apply builds its own parser per call and shares no mutable state; the returned tree is immutable.