Issue #1395974 by webbykat, Michelle, rdrh555: Clarify field_purge_batch() documentation.

core/modules/field/field.crud.inc

@@ -835,11 +835,12 @@ function field_delete_instance($instance, $field_cleanup = TRUE) {
 /**
  * Purges a batch of deleted Field API data, instances, or fields.
  *
- * This function will purge deleted field data on up to a specified maximum
- * number of entities and then return. If a deleted field instance with no
- * remaining data records is found, the instance itself will be purged.
- * If a deleted field with no remaining field instances is found, the field
- * itself will be purged.
+ * This function will purge deleted field data in batches. The batch size
+ * is defined as an argument to the function, and once each batch is finished,
+ * it continues with the next batch until all have completed. If a deleted field
+ * instance with no remaining data records is found, the instance itself will
+ * be purged. If a deleted field with no remaining field instances is found, the
+ * field itself will be purged.
  *
  * @param $batch_size
  *   The maximum number of field data records to purge before returning.