if the createIndexes has the following syntax:

db.runCommand(
    { createIndexes: <collection name>,
      indexes: 
         [
            {
                key: <key spec>,
                name: <idx name> ,
                ns: <namespace>
            }
         ]
    }
)

such that you always specify the single collection and the db would be the database you run the command on, why have the optional ns field? since if it doesn't match the database and the collection name, it gives you

"errmsg" : "namespace mismatch"

Wouldn't the user always just omit it?