Deprecated and ignored: the record of visited objects is now scoped to a single call, so it does not need trimming.
Control how many nested levels deep will be used, -1 = no limit, >-1 = nth level limited.
Deprecated and ignored: see mapLimit.
A predetermined list of references (source and the object it should resolve to) which every call starts from. It is only read, never added to.
Perform a deep merge of objects. This will return a function that will combine all objects and sub-objects. Objects having the same attributes will overwrite from last object to first. Every call of the returned function keeps its own record of the objects it has already visited (so circular references are followed only once, and an object which is referenced in several places is merged once), and nothing is remembered between calls: the results of separate calls never share state or go stale.