# Match documents where `field` matches `pattern`
	#
	# To read more about the available options, see:
	# https://docs.mongodb.com/manual/reference/operator/query/regex/#op._S_regex
	#
	# ~~~json
	# {field: {$regex: 'pattern', $options: '<options>'} }
	# ~~~
	#
	# Provides regular expression capabilities for pattern matching strings in queries.
	# MongoDB uses Perl compatible regular expressions (i.e. "PCRE" ).
	fun regex(field: String, pattern: String, options: nullable String): MongoMatch do
		var q = new JsonObject
		q["$regex"] = pattern
		if options != null then q["$options"] = options
		self[field] = q
		return self
	end