+
+ # Apply unwind
+ #
+ # https://docs.mongodb.com/manual/reference/operator/aggregation/unwind/
+ #
+ # Deconstructs an array field from the input documents to output a document
+ # for each element.
+ # Each output document is the input document with the value of the array
+ # field replaced by the element.
+ #
+ # ~~~json
+ # { $unwind: <field path> }
+ # ~~~
+ fun unwind(path: String): MongoPipeline do return add_stage("unwind", path)