Selection MaskingKeyCreator \ General-Interface \ Selection \ Selection-Masking
Selection Masking has been expanded to include solids and surfaces, Vectors, Planes and former ADM entities now integrated into the Dimension Menu. 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. You can 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. It simply acts temporarily to give you more control over your selection of geometry.
The Set Mask function can be accessed from the Edit pull-down menu. See Set Mask for more information.