Schemas should be able to define counter-examples (and the test suite should test those)

[gnidan]

JSON Schema is nice because it gives us a mechanism for specifying example values for schemas.

It does not, sadly, afford a way to specify illustrative counter-examples, but we can invent a field for this (since JSON Schema allows adding additional fields other than what's defined). Maybe this should be called counterExamples or x-counterExamples.