anchor.diff:  =====
   
   `metrics`::
  -(Required, array of objects)
  +(Required, object or array of objects)
   Collects and stores metrics for <<number,numeric>> fields. You must specify at
   least one `metrics` object.
   +
  
positive.code: [%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.
  
negative.code: [%collapsible%open]
  ======
  `fields`::
  (Required*, string or array of strings)
  <<number,Numeric>> fields to group. If you specify a `histogram` object, this
  property is required.
  +
  WARNING: Do not use the same fields in `histogram` and `metrics`. If you specify
  the same field in both `histogram` and `metrics`, the rollup attempt will fail.
  
  `interval`::
  (Required*, integer)
  