The handle back returns for a screen of Kind opened from Origin — the
frame below it, typed. For a screen that is the opener itself, or an item's
host when the edge was taken from an item; an inner tab closes together with
the screen it replaced, so its back is the frame below that screen. An
edge's handle passes the screens that can open it here
(ScreenOpenersOf, ScreenItemOpenersOf).
undefined is not a success: back on the only open frame is
ScreenRootBackError, so an inner tab that replaced the tab root (or a
screen root) yields never — the call can only fail at run time.
The handle
backreturns for a screen ofKindopened fromOrigin— the frame below it, typed. For a screen that is the opener itself, or an item's host when the edge was taken from an item; an inner tab closes together with the screen it replaced, so itsbackis the frame below that screen. An edge's handle passes the screens that can open it here (ScreenOpenersOf, ScreenItemOpenersOf).undefinedis not a success:backon the only open frame isScreenRootBackError, so an inner tab that replaced the tab root (or a screen root) yieldsnever— the call can only fail at run time.