anchor.diff:  Returns a list containing all current known data providers. This list can be extended in the future.
   
   
  -**NOTE**: The **locatedWithin** parameter has to be encoded before putting it to the request. If you do not, you will receive **empty** response with status code **400 Bad Request**.
  +### Cache control headers:
  +
  +The service offer regular HTTP caching hints in the reponse header.
  +All clients are requested to follow good API citizen guidelines and respect these cache information.
  +
  +Example: f data unchanged since this date using the If-Modified-Since request header
  +the server will return with an empty body with the 304 response code. Ex:
  ++ Last-Modified: Mon, 10 Jul 2017 08:37:16 GMT
  ++ If-Modified-Since: Thu, 13 Jul 2017 10:55:53 GMT
  
positive.code: required scope is `station-metadata`.
  
  The documentation about how to authenticate against MeteoGroup Weather API with
  OAuth 2.0 can be found here: [Weather API documentation](https://github.com/MeteoGroup/weather-api/blob/refactor-2-guideline/authorization/Authentication.md)
  
  ### Cache control headers:
  
  if data unchanged since this date using the If-Modified-Since request header
  the server will return with an empty body with the 304 response code. Ex:
  + Last-Modified: Mon, 10 Jul 2017 08:37:16 GMT
  + If-Modified-Since: Thu, 13 Jul 2017 10:55:53 GMT
  
  ### Querying MeteoGroup stations data
  
  
negative.code:         + hasObservationData: `true` (boolean, optional) - station has observation data.
          + countryIsoCode: `GB` (string, optional) - station located in this country. ISO Code refers to the [ISO 3166 alpha-2 codes](https://en.wikipedia.org/wiki/ISO_3166)
  
  The API supports various combinations for querying stations data by area/region (bounding box, polygon, multi-polygon), by provider or type,
  by stations where MeteoGroup produces forecast or has observation data available.
  Here are a couple of examples how to query by provider and type, bounding box and polygon.
  
  #### Querying by provider or type
  
  Query example:
  
  