Though an uncommon case, it's possible for a user to compare object literals directly using JSON Schema's enum keyword:

{enum: [{a: 1, b: 1}]}

This will currently use MongoDB's object comparison semantics, which takes field order into account. However, RFC 7159 §1 states that:

An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.

This implies that $jsonSchema object-to-object comparisons should be done without regard to field order, as JSON Schema adheres to the JSON spec.