Support for parsing a "database" key in the options array was introduced by d017a80 for PHPC-229; however, this option was never documented for MongoDB\Driver\Manager::__construct().

Historical note: In the legacy driver, MongoClient::__construct() did accept a "db" key in the options array.

We should either remove support for this option or document it. To my knowledge, the mongoc_uri_t.database string is only used by mongoc_client_get_default_database(), which we do not utilize. It may be returned by mongoc_uri_get_auth_source() in the absence of an "authsource" URI option (as noted in the Connection URI docs).