Attempts to subtract either months or years results in add instead of subtract. Other options - seconds, minutes, hours, days and weeks, work as expected. Sample code and output:
var d = DOpus.create.date();
DOpus.output(d);
var dadd = d.clone;
dadd.add(1,"y");
DOpus.output(dadd);
var dsub = d.clone;
dsub.sub(1,"y");
DOpus.output(dsub);
23/11/2016 14:58:13
23/11/2017 14:58:13
23/11/2017 14:58:13 - Should be 2015
Regards, AB