anchor.diff:  
   Array of failures if there were any unrecoverable errors during the process. If
   this is non-empty then the request aborted because of those failures.
  -Update-by-query is implemented using batches and any failure causes the entire
  -process to abort but all failures in the current batch are collected into the
  +Update by query is implemented using batches. Any failure causes the entire
  +process to abort, but all failures in the current batch are collected into the
   array. You can use the `conflicts` option to prevent reindex from aborting on
   version conflicts.
   
  
positive.code: returned by the failing bulk request are returned in the `failures` element; therefore
  it's possible for there to be quite a few failed entities.
  
  If you want to simply count version conflicts not cause the `_update_by_query`
  to abort you can set `conflicts=proceed` on the url or `"conflicts": "proceed"`
  in the request body. The first example does this because it is just trying to
  pick up an online mapping change and a version conflict simply means that the
  conflicting document was updated between the start of the `_update_by_query`
  and the time when it attempted to update the document. This is fine because
  that update will have picked up the online mapping update.
  
negative.code: [[docs-update-by-query-cancel-task-api]]
  === Works with the Cancel Task API
  
  Any update by query can be cancelled using the <<tasks,Task Cancel API>>:
  
  [source,js]
  --------------------------------------------------
  