+ /**
+ * Responds to a mouse wheel movement by scrolling the annotations up or down.
+ * Annotation labels are scrolled via method adjustmentValueChanged when the
+ * vertical scrollbar is adjusted.
+ * <p>
+ * If shift is pressed, then scrolling is left or right instead, and is
+ * delegated to AlignmentPanel, so that both sequences and annotations are
+ * scrolled together.
+ * <p>
+ * This object is a MouseWheelListener to AnnotationLabels, so mouse wheel
+ * events over the labels are delegated to this method.
+ * <p>
+ * Note that this method may also be fired by scrolling with a gesture on a
+ * trackpad.
+ */