void beginSelectionSequence(FieldLocation point) {
			if (!selectionOn) {
				return;
			}
			removeFromSelection = false;
			anchorPoint = new FieldLocation(point);
		}
Checks if the "control" modifier is on and the "shift" modifier is not.
Ghidra/Framework/Docking/src/main/java/docking/widgets/fieldpanel/FieldPanel.java