In V11 partitions are present, but not quite as visible as in prior versions.
Partitions and top level folders mirror each other.
When a partition is created a top level folder is created
tmsh create auth partition abc
Will create a partition and will also create the folder /abc.
tmsh list sys folder /abc
When a top level folder is created a corresponding partition will also be created.
tmsh create sys folder /efg
Will create the folder and also create a partition
tmsh list auth partition /efg
The cd command is used to move to a different partition.
tmsh cd /efg (you are now in the /efg folder and the efg partition)
tmsh create sys folder /efg/xzy
tmsh cd /efg/xyz (you are in the /efg/xyz folder and still in the efg partition)