An application typically tracks the modification state of a
document. A common reason to do so is to inform the user that they
have made changes to the document which they might wish to save
before closing the window.
When your application uses proxy icons, it should inform the
Window Manager when a document has unsaved changes. When you do
so, the Window Manager displays the document’s proxy icon in a
disabled state and prevents the user from dragging the proxy icon.
Disabled proxy icons cannot be dragged because unsaved documents
cannot be moved or copied in a manner predictable to the user.
Figure 1-3 shows a proxy icon in a document window with unsaved
Low contrast indeed. What a joyful little feature this was (and could be again). Clarity is the ideal that the Mac user interface used to celebrate but now largely ignores. I crave its return.