The Matte Opacity value is ignored, and all the matte for this fluid is set to be transparent. Use this option when you use substitute geometry in a scene to stand in for objects in a background image that you will be compositing with later. Your stand-in objects will ‘punch a hole’ in the matte. This allows other computer-generated geometry to pass behind your stand-in objects. Later, when foreground and background are composited, the results will be correct, with the background object showing through the ‘black hole’ areas.

影像形板不透明值可忽略不计，而所有流体影像形板设置为透明状态。当你使用场景中的替代几何体替换一个稍后要合成的背景图像中的对象时，你要使用此选项。你的替身对象将在影像形板中“钻一个孔”。这会使得计算机生成的其他几何体从你的替身对象后面通过。稍后，随着前景和背景的合成，背景对象会通过'黑洞'区域显示出来，各种结果会是正确的。

（供参考）