merge

Merge other into this config in place: every entry from other's two maps is copied into this config's maps, with later puts overwriting earlier keys. This is how the global → presentation → slide cascade resolves (parent merged first, then child).

Values are copied by reference — a collection-valued option (e.g. a Map/List) is shared with other, not deep-copied. That is safe because config collection values are only ever replaced, never mutated in place. Note this is distinct from (and name-collides with) the Map.merge extension elsewhere; this one mutates the receiver rather than returning a new map.