Determinism and portability
Determinism
Section titled “Determinism”A mapping over a given input produces the same output every time, under two
conditions. The keywords in play are deterministic: everything Core and
Extended is, while random and unique are Experimental precisely because
they are not. And the registered extensions are pure: a plugin that fetches,
a transformer that reads a clock, an initializer that mints UUIDs each
introduce exactly the nondeterminism they contain.
Both sources are visible. Nondeterministic keywords are named in the document; impure extensions are named in the registration. A reader can audit a mapping’s determinism without running it.
One structural requirement supports this: mappings are ordered maps. Pairing order is semantics, so the document must reach the evaluator with its key order intact. Standard YAML and JSON parsers preserve insertion order; anything that round-trips through an unordered structure corrupts the program.
Portability
Section titled “Portability”The Core tier is the portable surface: any conforming implementation runs Core documents identically. Extended keywords are optional but exact where present. Experimental keywords carry no cross-implementation guarantee.
For mapper-js specifically, the released engine conforms to the specification everywhere its conformance suite probes, as of 0.2.0. Two narrow diagnostics are still to come (SPEC Appendix A), and these docs mark them where they matter. Every example here runs against the published package, so what you read is what you get.