The winding rule describes how a path is filled (if it has a fill colour). The winding rule can be either even-odd or non-zero. Figure 9.14 illustrates the difference between the two winding rules. A path was constructed with a gap between the outer and inner rectangles. Figure 9.14(a) shows the effect using the even-odd winding rule and Figure 9.14(b) shows the effect using the non-zero winding rule. The winding rule is also used when extracting the parameters for \parshape and \shapepar.