A container lets you mask images or other elements. This can be useful if you need to clip an image or animate the clipping of an image. For example, you can make the boundary of the container expand, revealing more of the element.
To create a mask
Select your image or elements, then up the top and center select Mask.
This will wrap your selection inside a mask. You’ll notice a dashed bounding box around your element. Adjusting the size of your mask will mask the layers nested within it.
Masks can be styled with a background color, border, border radius, opacity and shadow.
To directly select any element within a mask, hold Cmd and click the element. This will reveal any elements outside the container boundary, making it easy to reposition elements or see what’s inside the mask.
To release a mask's elements, Ungroup it by using the ungroup keyboard shortcut (Cmd + Shift + G) or selecting Ungroup from the top menu.
Recommended Reading: Using masks in animation
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