The $changeStreams parameter description for $_passthroughToShard says that if a shard key is provided, then a shard will be targeted. Mentioning `shard key` in this context is wrong since the only shards can be specified under the $_passthroughToShard parameter.

Therefore, the description needs to be rephrased to something similar to:

An optional internal parameter for this request. If a shard is specified, then that specific shard will be targeted.