Optional ReadonlypromoteWhich feature property the engine promoted to the feature id, when any.
Read rather than mirrored in the layer registry, and that is deliberate: the
source IS the record of this fact, it answers in O(1), and a mirror would drift —
transformStyle recreates every source on a basemap switch.
OptionalupdateApplies a partial update. Optional: the guard typeof source.updateData === "function" is what decides the diff path, and a test double that omits it
legitimately exercises the fallback.
Structural view of a MapLibre GeoJSON source's mutating methods. The registry stores generic
Sourcehandles; the adapter narrows to this shape (guarded bytypeof source.setData === "function") before replacing layer data.