a section of the curve as an array of points</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>index</code> - the curve index specifying the curve to analyse</dd>
<dd><code>start</code> - the start position of the curve segment (0.0...1.0)</dd>
<dd><code>end</code> - the end position of the curve segment (0.0...1.0)</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>a sequence of point representing the curve section or null
                        if it cannot be calculated<