A few questions about the documentation of connPoolMaxShardedConnsPerHost parameter

1) Is this limit per target host (connected from mongos) or is it for the mongos server in total?
2) Is this connPoolMaxConnsPerHost parameter required for connPoolMaxShardedConnsPerHost? On a shard router do both parameters need to be set?
3) Is there only one pool per server or does it depend on the number of cores?