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 invert any surface using the toggle under the "PATHS" menu item.