anchor.diff:  in order to finish it. Otherwise they may retrieve a list of
   classifications from the Classification Collection resource.
   
  ++ Request
  +
  +    + Headers
  +
  +            Accept: application/vnd.api+json; version=1
  +            Content-Type: application/json
  +
   + Response 200
   
       [Classification][]
  
positive.code: + Parameters
    + id (required, integer) ... id of workflow to update
  
  + Request (application/vnd.api+json)
  
          { "subject_sets": ["9"] }
  
  + Response 200
  
  
negative.code: project content models.
  
  Project Contents that have the same language as their parent project's
  primary_language field may not be destroyed.
  
  + Request
  
      + Headers
  
              Accept: application/vnd.api+json; version=1
              Content-Type: application/json
  
  + Response 204
  
  