Selection tools and Mask Editor
The selection tools are powerful tools to apply masks to video effects. This allows you to create limits, opacities and animations on both layers and video effects/transitions. You can have geometric masks and brush masks.

An example of a geometric mask. Only part of the image is changed.

You have 8 geometric tools and 1 bitmap brush tool: These tools work in 3 ways: The geometric masks can also be transformed (widened, translated, rotated, scaled, outlined).

The brush tool can help you to create a bitmap opacity brush. Selecting this tool will cancel all geometric masks and present you a drawing interface in which you have drawing tools (rectangle, circle, fill) along with a radius, strength and opacity selector. The more close the opacity is to 1.0 (full), the more the brushed area masks the layer.