message: Document upgrade path for count operators
diff: @@ -393,6 +393,21 @@ class MONGOCXX_API collection {
  /// This method has been deprecated in favor of count_documents() and
  /// estimated_document_count().
  ///
  + /// When migrating to count_documents() the following query operators must be replaced:
  + ///
  + /// [$expr]: https://docs.mongodb.com/manual/reference/operator/query/expr/ "$expr"
  + /// [$geoWithin]: https://docs.mongodb.com/manual/reference/operator/query/geoWithin/ "$geoWithin"
  + /// [$center]: https://docs.mongodb.com/manual/reference/operator/query/center/#op._S_center "$center"
  + /// [$centerSphere]: https://docs.mongodb.com/manual/reference/operator/query/centerSphere/#op._S_cent "$centerSphere"
  + ///
  + /// Operator | Replacement
  + /// -------------|----------------------------------
  + /// $where | [$expr]
  + /// $near | [$geoWithin] with [$center]
  + /// $nearSphere | [$geoWithin] with [$centerSphere]
  + ///
  + /// $expr requires MongoDB 3.6+
  + ///
  /// @param filter
  /// The filter that documents must match in order to be counted.
  /// @param options
  @@ -417,6 +432,21 @@ class MONGOCXX_API collection {
  /// This method has been deprecated in favor of count_documents() and
  /// estimated_document_count().
  ///
  + /// When migrating to count_documents() the following query operators must be replaced:
  + ///
  + /// [$expr]: https://docs.mongodb.com/manual/reference/operator/query/expr/ "$expr"
  + /// [$geoWithin]: https://docs.mongodb.com/manual/reference/operator/query/geoWithin/ "$geoWithin"
  + /// [$center]: https://docs.mongodb.com/manual/reference/operator/query/center/#op._S_center "$center"
  + /// [$centerSphere]: https://docs.mongodb.com/manual/reference/operator/query/centerSphere/#op._S_cent "$centerSphere"
  + ///
  + /// Operator | Replacement
  + /// -------------|----------------------------------
  + /// $where | [$expr]
  + /// $near | [$geoWithin] with [$center]
  + /// $nearSphere | [$geoWithin] with [$centerSphere]
  + ///
  + /// $expr requires MongoDB 3.6+
  + ///
  /// @param session
  /// The mongocxx::client_session with which to perform the count.
  /// @param filter
  