, there must be
            one or more calls to <a class="citerefentry" href="gluTessBeginContour"><span class="citerefentry"><span class="refentrytitle">gluTessBeginContour</span></span></a>/<a class="citerefentry" href="gluTessEndContour"><span class="citerefentry"><span class="refentrytitle">gluTessEndContour</span></span></a>.
            Within each contour, there are zero or more calls to <a class="citerefentry" href="gluTessVertex"><span class="citerefentry"><span class="refentrytitle">gluTessVertex