openapi: 3.0.0
info:
  title: Sample API
  description: Optional multiline or single-line description in [CommonMark](http://commonmark.org/help/) or HTML.
  version: 0.1.9
servers:
  - url: http://api.example.com/v1
    description: Optional server description, e.g. Main (production) server
  - url: http://staging-api.example.com
    description: Optional server description, e.g. Internal staging server for testing
paths:
  /users:
    get:
      summary: Returns a list of users.
      description: Optional extended description in CommonMark or HTML.
      parameters:
        - in: query
          name: sort
          description: Sort order
          schema:
            type: string
            nullable: true
            enum:
              - asc
              - desc
              - null 
      responses:
        '200':
          description: A JSON array of user names
          content:
            application/json:
              schema: 
                type: string
                nullable: true
                enum:
                  - asc
                  - desc
                  - null