Issue #3277148 by rpayanm, andregp, joachim, Farnoosh, Athrylith, Jingting:...

Issue #3277148 by rpayanm, andregp, joachim, Farnoosh, Athrylith, Jingting: ResourceResponse should document that the route it is used with must define the _format requirement

(cherry picked from commit 58a50468)

core/modules/rest/src/ResourceResponse.php

@@ -14,6 +14,8 @@
  * string or an object with a __toString() method, which is not a requirement
  * for data used here.
  *
+ * Routes that return this response must specify the '_format' requirement.
+ *
  * @see \Drupal\rest\ModifiedResourceResponse
  */
 class ResourceResponse extends Response implements CacheableResponseInterface, ResourceResponseInterface {