Why does the JSON schema for 3.0 specify patternProperties for component names but allows additional properties?

Discussed in https://github.com/OAI/OpenAPI-Specification/discussions/2439

^{Originally posted by ryankinderman January 11, 2021}
I've been working on some functionality that uses the JSON schema to help validate OpenAPI schemas, and recently noticed that the 3.0 schema allows any value for {name} in /components/{component}/{name}, while the specification states that "All the fixed fields declared above are objects that MUST use keys that match the regular expression: ^[a-zA-Z0-9\.\-_]+$." It seems like this could have been validated automatically by simply adding additionalProperties: false to the JSON schema.

My question is: Was not including additionalProperties: false in the JSON schema for 3.0 just an accidental omission, or was there some rationale behind not doing it?

Thanks for clarifying!

Start with the 3.0 JSON schema and compare its component-name handling with the fixed-fields section of versions/3.0.3.md, then review discussion #2439 for the rationale. Done means documenting whether allowing additional properties is intentional or identifying the precise schema/spec correction.