# Apply projection
	#
	# https://docs.mongodb.com/manual/reference/operator/aggregation/project/#pipe._S_project
	#
	# Passes along the documents with only the specified fields to the next stage
	# in the pipeline.
	#
	# ~~~json
	# { $project: { <specifications> } }
	# ~~~
	#
	# The specified fields can be existing fields from the input documents or
	# newly computed fields.
	fun project(projection: JsonObject): MongoPipeline do return add_stage("project", projection)