Collation allows users to specify language-specific rules for string comparison, such as rules for letter-case and accent marks.
Users can specify an arbitrary string to help trace the operation through the database profiler, currentOp, and logs.
The index to use. Specify either the index name as a string or the index key pattern.
Map of parameter names and values. Values must be constant or closed expressions that do not reference document fields. Parameters can then be accessed as variables in an aggregate expression context (e.g. "$$var").
A document that expresses the write concern of the insert command. Omit to use the default write concern.