Layer Mask

Show Hide To Enable Layer Masking:

Open Artboard > Preferences… Editing in the main menu.
Check "Enable Layer Mask Commands". Mask commands will be made available in Layers > Mask in the main menu.

Show Hide To Add a Shape to a Layer Mask:

Select a layer in the Layers panel that contains the objects you want to mask.
Draw one or more shape objects on the layer to be used as the mask (image 1).
With the masking object(s) selected, choose Layer > Mask > Add To Layer Mask.

4. The masked area is initially displayed with a semi-transparent checked-pattern, hiding the drawing objects underneath. The original masking object(s) is not automatically removed from the drawing (image 2) – move or delete the masking object(s) as desired.
5. When you are satisfied with the layout of the mask, choose Layer > Mask > Hide Layer Mask to visually remove the checkered mask area.

HINT: A Layer Mask is a visual effect applied only to the objects on a single layer. In this example (image 3), a Layer Mask is applied to the "background" layer of buildings, while the figure is on a separate drawing layer on top that is not masked.

Show Hide To Clear a Mask from a Layer:

Select the layer with the mask you want to remove in the Layers panel.
Choose Layer > Mask > Clear Mask.

Show Hide To Add Additional Shapes to the Layer Mask:

Select the layer with the mask you want to add to in the Layers panel.
Draw another shape to add to the existing mask area.
With the masking object(s) selected, choose Layer > Mask > Add To Layer Mask.

Show Hide To Subtract Areas From an Existing Layer Mask:

Select the layer with the mask you want to subtract from in the Layers panel.
Draw a shape(s) to subtract from the existing mask area (it should overlap the existing mask area).
With the masking object(s) selected, choose Layer > Mask > Subtract from Layer Mask.

Show Hide Note on Using Text and Paths in Layer Mask:

Convert text before adding to layer mask by selecting the text and choosing Graphic > Convert To Path or Graphic > Convert To Shape.
Outline paths before adding to layer mask by selecting the path(s)and choosing Edit > Path > Outline.

Show Hide To Disable (or Enable) a Layer Mask:

Select the layer with the mask you want to disable (or enable) in the Layers panel.
Choose Layer > Mask > Disable (or Enable) Layer Mask.

Show Hide To Hide (or Show) the Layer Mask's Checkered Mask Area:

Select the layer with the mask you want to hide (or show) in the Layers panel.
Choose Layer > Mask > Hide (or Show) Layer Mask.