Mariner Software StoryMill for Mac - Manual (Page 59)

Window fading
You may find yourself at times wishing to reference information
outside of StoryMill while you write. While you can always use
command-tab and so forth to switch to other applications to
reference them, StoryMill also provides the option to fade almost
any of its windows. Fading causes the window to become highly
transparent (just how transparent is configurable in the
General
preferences ; see p. 61). To use window fading, you can either add
the custom toolbar button or choose Window→Fade Window.
If you want to use the toolbar button, right click anywhere on the
toolbar (in either the chapter editing window or the project window)
or choose View→Customize Toolbar…. Drag the Fade button
from the sheet to the toolbar:
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