Click Accept after
selecting all letters if you want to create a single mask shape.
or
Click Accept after
selecting each letter if you want to create separate mask shapes
for each letter.
To protect the text area on the canvas
from being over-painted, no further action is necessary. To modify
the paint on the text area only, click on the MaskShape-# layer
in the Canvas Layer Editor, and choose Invert
layer from the editor’s Edit menu.