Debug Modifier  调试修整
用于这个子树（大括号内的模型）就像普通的一样渲染过程，但是同样画一个没有修整的转换粉色。
Usage example:
# { ... }
案例代码 :

difference() {
// start objects
cylinder (h = 4, r=1, center = true, $fn=100);
// first object that will subtracted
# rotate ([90,0,0]) cylinder (h = 4, r=0.3, center = true, $fn=100);
// second object that will be subtracted
# rotate ([0,90,0]) cylinder (h = 4, r=0.9, center = true, $fn=100);
}