What are you using this for and could you elaborate a bit more?
As I read it from the manual it says:
"Splits the simulation in a training period (given in percent) and a following test period. F.i. when set at 60, the training period has a length of 60% and the test period has a length of 40%. This works with or without WFO and ensures that the test always uses out-of-sample data."
So, if you are asking if
DataSplit = 90;
will split your data into 90% training data and 10% test data, then yes.