title: How to reference top-level parameters in Swagger 2.0
body: <p>I'm trying to figure out how to use top level parameters and then, at the operation level,use a $ref to refer to the definition that was declared at the top level object.</p>
  
  <p>Here is what the YAML looks like but when I try this I get an empty parameter displayed. Anyone know the correct syntax for this?</p>
  
  <pre><code>swagger: '2.0'
  info:
    version: 0.1.0
    title: Customer API
  parameters:
    index:
      name: index
      in: query
      description: Specifies the offset of the first item to be returned. The default value is 0, which starts at the beginning.
      type: integer
      default: 0
      minimum: 0
  paths:
    /customers:
      get:
        parameters:
          - $ref: '#/parameters/index'
        responses:
          200:
            description:  List all customers
            schema:
              $ref: '#/definitions/Customers'
  definitions:
    Customer:
      properties:
        name:
          type: string
        id:
          type: integer
          format: int32
    Customers:
      properties:
        startIndex:
          type: integer
        itemsPerPage:
          type: integer
        totalResults:
          type: integer
        entries:
          type: array
          $ref: Customer
  </code></pre>