get: 
  tags:
    - Population statistics
  operationId: groupByItems
  summary: Group-by items
  responses:
    200:
      description: |-
        Returns a list of all available group-by items for the _population group-by end point_, but only if the items are available for the selected customer. A customer is selected by a JWT-claim or the AGB header. The output of this end point should be the same as the documentation for the groupByItems-parameter of the mentioned end point. 
      content: 
        application/json:
          schema:
            type: array
            items: 
              type: string
            example:
              - age
              - preferredDoctor
              - insurer
              - gender
              - deprivedNeighborhood
    400:
      $ref: '../zoo-api.yaml#/components/responses/ReqFailure'
    401:
      $ref: '../zoo-api.yaml#/components/responses/JwtFailure'
    404:
      $ref: '../zoo-api.yaml#/components/responses/PatNotFound'