public AxisStack (ForwardAxis faxis, ActiveAxis parent) {
this.subtree = faxis;
this.stack = new ArrayList();
this.parent = parent; // need to use its contextdepth each time....
// improvement:
// if ! isDss, there has nothing to do with Push/Pop, only one copy each time will be kept
// if isDss, push and pop each time....
if (! faxis.IsDss) { // keep an instance
this.Push (1); // context depth + 1
}
// else just keep stack empty
}