Just to be clear - the `partitionSelectorClass` contains the name of a class that calculates the partition, whereas `partitionSelectorExpression` returns a **hash** that is in turn used to calculate the partition...is this correct? If so should this be named `partitionHashSelectorExpression` or something along those lines? I found this a bit confusing since the name `partitionSelectorExpression` seems to indicate that the expression itself is responsible for calculating the partition.