Extract Mask tool

In Sculpting using the F MASK brush I intend to mask areas and then extract new volumes of them, I am doing it using the multires modifier, but I do not see the option Extract Mak, How do I extract volumes?
The Extract Mask tool is seen in this video in 1:07 seconds …

regards

The tool in the video is from an addon https://blenderartists.org/forum/showthread.php?316520-Sculpt-Tools