Question about mongo cluster connection string

i read mongodb document which says the mongo cluster with multi mongos , url should be:
my question is: if mongos0 is not available, client or program will auto connect to mongos1 ?
or all client connections will be load balance between three mongos?

Does the client connect to the first mongos if there are multi mongos in the connection string ?
if that is true, say i have many client applications, should i put different mongos in the first position for different client applications for load balance .