anchor.diff:  data requires special support because time-based intervals are not always a
   fixed length.
   
  +Like the histogram, values are rounded *down* into the closest bucket. For
  +example, if the interval is a calendar day, `2020-01-03T07:00:01Z` is rounded to
  +`2020-01-03T00:00:00Z`. Values are rounded as follows:
  +
  +[source,java]
  +----
  +bucket_key = Math.floor(value / interval) * interval)
  +----
  +
   [[calendar_and_fixed_intervals]]
   ==== Calendar and fixed intervals
   
  
positive.code: --------------------------------------------------
  // TESTRESPONSE[s/\.\.\./"took": $body.took,"timed_out": false,"_shards": $body._shards,"hits": $body.hits,/]
  
  ===== Timezone
  
  Date-times are stored in Elasticsearch in UTC.  By default, all bucketing and
  rounding is also done in UTC. Use the `time_zone` parameter to indicate
  that bucketing should use a different timezone.
  
  You can specify timezones as either an ISO 8601 UTC offset (e.g. `+01:00` or
  `-08:00`)  or as a timezone ID as specified in the IANA timezone database,
  such as`America/Los_Angeles`.
  
  Consider the following example:
  
  
negative.code: 
  In contrast to calendar-aware intervals, fixed intervals are a fixed number of SI
  units and never deviate, regardless of where they fall on the calendar. One second
  is always composed of `1000ms`. This allows fixed intervals to be specified in
  any multiple of the supported units.
  
  However, it means fixed intervals cannot express other units such as months,
  