This enables VoiceOver user to see the document view as a single
element and interact with it (i.e. inspect its subelements) only when
needed by using the VO-Shift-down shortcut (and stop interacting with
it using VO-Shift-up shortcut). This makes the element structure more
hierarchical where at the top level are only major user interface
components, so that it's easier for orientation. It also prevents
unrelated UI elements to be sequential as VoiceOver by default orders
elements by the visual order (top-down, left-right) rather then
the order in the AXChildren array. For example in this case,
the bottom status bar of the document window gets separated from
the bottom toolbar of the file browser, unlike the situation before
grouping when both bars were adjacent to the VoiceOver user.
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