This behavior has changed as of Lightform Creator version 2.1.4 released on March 31, 2021
Paths in a surface now have selectable boolean operations - This makes it easy to combine paths in flexible ways, such as subtracting one path from another. Pro-tip: When merging surfaces, keep track of each path by selecting "Auto-Name Paths" to have the path name reflect the surface name. Read more about these operations here.
With "Labs" enabled, you can add and subtract pen paths from existing surfaces. See the below video for a quick demonstration.
You can make very complex masks quickly by layering these actions. For example, selecting the water and the whale from this painting would have been very difficult, but by using the "PATHS" dialog, it takes only a few seconds.