The
command lets you toggle between showing the layer and showing the layer mask. When a layer mask is shown you can perform paint operations on it without touching the layer itself.Although this command can be used to enable showing layer masks for multiple layers, only one of the layer masks will be shown at a time. To view another layer mask, the currently shown layer mask will need to be toggled off first, using the same command as used to show it. When a layer mask is in «show mode» its thumbnail in the Layers Dialog is shown with a green border.
You can access this command
From the main menu through
→ → .From the Layers Dialog, you can access it through the command of its context menu; or by holding down the Alt key and clicking on the layer mask's thumbnail in the Layers Dialog.