Set MaskKeyCreator \ Edit \ Set-Mask
Selection Masking includes Solids, Surface, Planes and Detail Menu elements. When you are working on complex parts that are made up of densely packed entities, masking allows you to focus on the specific entities you want to select. Think of masking as a transparent overlay that filters out the entities you do not want. This makes the entities you do want easier to access. This transparent filter does not, in any way, alter your drawing
The Mask function can be accessed from the Edit pull-down menu, or from the Immediate commands under Tools>Options>Commands.