anchor.diff:  NOTE: The `avg` metric stores both the `sum` and `value_count` values. This lets
   you accurately average rollups over larger time intervals. For example, you can
   accurately roll up hourly averages into daily averages.
  -====
  +=====
   
   `page_size`::
   (Optional, integer)
  
positive.code: +
  .Properties of `terms`
  [%collapsible%open]
  =====
  `fields`::
  (Required*, array of strings)
  Array of <<keyword,keyword family>> and <<number,numeric>> fields to store. If
  you specify a `terms` object, this property is required.
  +
  TIP: Avoid storing high-cardinality fields. High-cardinality fields can greatly
  increase the size of the resulting rollup index.
  =====
  ====
  
  `metrics`::
  (Optional, array of objects)
  
negative.code: +
  .Properties of `histogram`
  [%collapsible%open]
  ======
  `fields`::
  (Required*, array of strings)
  Array of <<number,numeric>> fields to group. If you specify a `histogram`
  