ode> draws vertical lines at the position of each of the axes.</li>
<li>
<code>geom_pcp_boxes</code> draws rectangles framing each level of a categorical variable. The parameter <code>boxwidth</code> specifies the width of these rectangles (1 is the width between successive variables). <code>boxwidth</code> is set to 0.2 by default.</li>
<li>
<code>geom_pcp_labels</code> places a label center on each rectangle of a categorical variable. XXX The familiar parameters <code>nudge_x</code> and <code>nudge_y</cod