x-fern-enum
`x-fern-enum` appears on schema objects and properties. Its value is a structured object. Used by 3 providers across 10 OpenAPI documents. It sits in the `x-fern-` namespace, so its meaning is defined by fern tooling rather than by OpenAPI. Consistent with type system — this is inferred from where the key appears and what it carries, not from any published definition.
Where it appears
| Location in the document | Occurrences | |
|---|---|---|
| schema | 13 |
What its value looks like
| Value shape | Occurrences |
|---|---|
| object | 13 |
Providers publishing it
All 3.
Why this is not in OpenAPI
Extensions exist because a provider needed something the specification would not carry. Most of what they hold is not the API contract at all — it is operational metadata about the contract: documentation, lifecycle, policy, provenance, and now agents. That metadata is usually better placed alongside the contract, in an Overlay or an APIs.json index, than crammed inside it. See everything else doing the data & schema semantics job.