throw new IllegalArgumentException("Require weight >= 1.");
}
// store the plot and its weight
subplot.setParent(this);
subplot.setWeight(weight);
subplot.setInsets(new RectangleInsets(0.0, 0.0, 0.0, 0.0));
subplot.setRangeAxis(null);
subplot.setOrientation(getOrientation());
subplot.addChangeListener(this);
this.subplots.add(subplot);
// configure the range axis...