anchor.diff:  ==== Missing Values
   
   The `missing` parameter specifies how docs which are missing
  -the field should be treated: The `missing` value can be
  +the sort field should be treated: The `missing` value can be
   set to `_last`, `_first`, or a custom value (that
   will be used for missing docs as the sort value).
   The default is `_last`.
  
positive.code: ==== Ignoring Unmapped Fields
  
  By default, the search request will fail if there is no mapping
  associated with a field. The `unmapped_type` option allows to ignore
  fields that have no mapping and not sort by them. The value of this
  parameter is used to determine what sort values to emit. Here is an
  example of how it can be used:
  
negative.code: [[search-request-sort]]
  === Sort
  
  Allows you to add one or more sorts on specific fields. Each sort can be
  reversed as well. The sort is defined on a per field level, with special
  field name for `_score` to sort by score, and `_doc` to sort by index order.
  
  