---
user:
  get:
    parameters:
      - $ref: "#/parameters/id_ref"
    responses:
      200:
        description: A user
        schema:
          $ref: "#/x-def/User"

parameters:
  id_ref:
    $ref: "#/parameters/id"
  id:
    in: path
    name: id
    required: true
    type: string

x-def:
  User:
    properties:
      name:
        type: string
