# Array element match
	#
	# https://docs.mongodb.com/manual/reference/operator/query/elemMatch/#op._S_elemMatch
	#
	# `$elemMatch` matches documents that contain an array field with at least
	# one element that matches all the specified query criteria.
	#
	# ~~~json
	# { field: { $elemMatch: <query> } }
	# ~~~
	fun elem_match(field: nullable String, query: Serializable): MongoMatch do
		op("elemMatch", field, query)
		return self
	end