title: Swagger 2.0 - how to make "one or the other" parameter required?
body: <p>I have a swagger 2.0 resource defined below. How can I make "param1 or param2" required? Caller has to pass either param1 or param2.</p>
  
  <pre><code>/some/res:
  put:
    summary: some resource
    responses:
      200:
        description: Successful response
        schema:
          $ref: '#/definitions/SomeResponse'
    parameters:
      - name: param1
        type: string
        description: param1
        in: formData
        required: false
      - name: param2
        type: string
        description: param2
        in: formData
        required: false
  </code></pre>