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This method is used to apply resource-specific knowledge on the exchange.
If the request was successful, it sets the Observe option for the
response. It is important to use the notificationOrderer of the resource
here. Further down the layer, race conditions could cause local
reordering of notifications. If the response has an error code, no
observe relation can be established and if there was one previously it is
canceled. When this resource allows to be observed by clients and the
request is a GET request with an observe option, the
ServerMessageDeliverer already created the relation, as it
manages the observing endpoints globally.