How to make an object visible only inside a rectangle

[Bendora]

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Masking Elements by using Content Overflow & Groups

(Below is one technique to mask content, here are a few more). Most commonly, groups are useful to keep elements organized and aligned as one unit as you arrange your animation. Groups can also be useful to animate a 2 or more elements in the same way: instead of animating multiple elements with the same keyframes, the keyframes can be set on the group. Masking is somewhat hidden feature of groups. Since each group has a rectangular shape, you can easily mask parts of the group by setting the…