Currently, any $jsonSchema validator expression which features a negation will simply state that the child expression or the schema matched (ex. given expression {$nor: [{$jsonSchema: {}}]} or {$jsonSchema: {not: {}}} and the document {}, you will get "schema matched" in the first case and "child expression matched" the second case). This ticket tracks the work necessary to make inversion provide detailed errors.

Note that this has a surprising amount of complexity, namely because of the semantics of various $jsonSchema keywords and the way that some keywords are translated into MatchExpression.