- |
  ## Identifier maps

  The schema may designate certain fields as having a `mapSubject`.  If the
  value of the field is a JSON object, it must be transformed into an array of
  JSON objects.  Each key-value pair from the source JSON object is a list
  item, each list item must be a JSON object, and the value of the key is
  assigned to the field specified by `mapSubject`.

  Fields which have `mapSubject` specified may also supply a `mapPredicate`.
  If the value of a map item is not a JSON object, the item is transformed to a
  JSON object with the key assigned to the field specified by `mapSubject` and
  the value assigned to the field specified by `mapPredicate`.

  ### Identifier map example

  Given the following schema:

  ```
- $include: map_res_schema.yml
- |
  ```

  Process the following example:

  ```
- $include: map_res_src.yml
- |
  ```

  This becomes:

  ```
- $include: map_res_proc.yml
- |
  ```
