Indicates the name of the data region, grouping, or data set for a sort.
Data type and length
0-1: Optional element that can occur once or not at all.
If omitted, the sort will apply to the instance of the current scope.
The sort target must be within the current scope, an ancestor scope, or a peer scope which is a data region.
A matrix grouping is only a valid SortTarget from within matrix grouping scopes along the same matrix axis.