")?

Specifically, I wonder if it is prohibited that, when Scheme implementation provides, e.g. tree-map object, to just add mapping APIs to tree-map, instead of creating a wrapper type.

This is probably a general question as we provide more datatypes in srfis; what scope the disjointness requirments cover?  If a future srfi provides another mapping-like APIs, should it be with disjoint types, rather than extending srfi-146 mappings?