Clarify discriminator non-impact on validation

[handrews]

• FixesOAS Dialect does not require the OAS vocabulary #3901 (discriminator-specific aspects)

Be very explicit that discriminator MUST NOT change the validation outcome, and explain the implication for the "allOf" use case.

[jam01]

Would you consider changing Schema Object # Properties

to go from

The OpenAPI Schema Object dialect is defined as requiring the OAS base vocabulary, in addition to the vocabularies as specified in the JSON Schema draft 2020-12 general purpose meta-schema.

to

The OpenAPI Schema Object dialect declares the OAS base vocabulary as optional, in addition to the vocabularies as specified in the JSON Schema draft 2020-12 general purpose meta-schema. When supported an implementation can optimize validation performance, but does not change the outcome as optional vocabularies do not directly impact validation.

Or something along those lines...?

[handrews]

@jam01 I'll handle that in the fix to issue #3877 which is about dialects specifically.

[handrews]

@jam01 although I probably won't go into that level of detail- more likely I will link to the JSON Schema documentation for $vocabulary.

[mikekistler]

Looks good. 👍