anchor.diff:  // tag::rollup-config[]
   `groups`::
   (Required, object)
  -Aggregates and stores fields in the rollup.
  +Aggregates and groups documents in the rollup.
   +
   .Properties of `groups`
   [%collapsible%open]
  
positive.code: 
  * You can only roll up an index that contains:
  
  ** A <<date,`date`>> or <<date_nanos,`date_nanos`>> timestamp field
  ** One or more <<number,numeric>> fields
  
  * If the {es} {security-features} are enabled, you must have the `manage`
  <<privileges-list-indices,index privilege>> for the index you roll up.
  
negative.code: <<search-aggregations-metrics-max-aggregation,`max`>>,
  <<search-aggregations-metrics-sum-aggregation,`sum`>>,
  <<search-aggregations-metrics-avg-aggregation,`avg`>>, and
  <<search-aggregations-metrics-valuecount-aggregation,`value_count`>>. <<date,`date`>> and <<date_nanos,`date_nanos`>>
  fields only support the `max`, `min`, and `value_count` metrics. You must specify
  at least one value.
  +
  NOTE: The rollup index stores these metrics in an
  <<aggregate-metric-double,`aggregate_metric_double`>> field. The `avg` metric
  