anchor.diff:   failures that are 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'd like to count version conflicts rather than cause them to abort then
  +If you'd like to count version conflicts rather than cause them to abort, then
   set `conflicts=proceed` on the url or `"conflicts": "proceed"` in the request body.
   
   Back to the API format, this will delete tweets from the `twitter` index:
  
positive.code: 
  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.
  Delete-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
  array. You can use the `conflicts` option to prevent reindex from aborting on
  version conflicts.
  
negative.code: are distributed proportionally to each sub-request. Combine that with the point
  above about distribution being uneven and you should conclude that the using
  `size` with `slices` might not result in exactly `size` documents being
  deleted.
  * Each sub-request gets a slightly different snapshot of the source index
  though these are all taken at approximately the same time.
  
  [float]
  