anchor.diff:  
   In the case of being present, the error payload is JSON object including the following fields:
   
  -* `error` (mandatory): a textual description of the error.
  -* `description` (optional): additional information about the error.
  -* `affectedItems` (optional): a list of elements affected by the error. Depending on the operation, it may
  ++ `error` (required, string): a textual description of the error.
  ++ `description` (optional, string): additional information about the error.
  ++ `affectedItems` (optional, array[string]): a list of elements affected by the error. Depending on the operation, it may
     refer to entities, registrations or subscriptions.
   
   Error list (HTTP response code in paranthesis):
  
positive.code: + Response 204
  
  
  ## Attribute Value by Entity ID [/v2/entities/{entityId}/attrs/{attrName}/value{?options}]
  
  ### Get attribute data [GET /v2/entities/{entityId}/attrs/{attrName}/value{?options}]
  
  
negative.code:             "duration": "PT1M"
          }
  
  
  ### Update subscription [PATCH /v2/subscriptions/{subscriptionId}]
  
  Only the fields included in the request are updated in the subscription.
  