Time for action — masking objects

Here are some quick steps to see what a mask will look like:

1. Use the same objects in an open Inkscape document as in the previous example. This time, however, let's make the background leaves black and the tree in front a grayscale color as follows:
   
2. Press Ctrl + A to select all objects on your canvas.
3. In the main menu select Object | Mask | Set.
   
4. In this result, the top object also becomes the overall shape, while the bottom peeks through. However, you will notice the degrees of grayscale setting over the entire object now. Masking depends only on grayscale. Thus, when using white, the objects below will be fully visible; when using black, the objects below will be fully blocked; and any gray level in between, the objects will be partially masked as in our example:
   

   Note

   Just like in a group, if you double-click a clip, you will be able to select and edit the objects within it.

5. One other item to note here is that the resulting masked object will have...