What a handle's back returns and may fail with: the framework's own method.
Like every member of a handle it runs with the services held when the
screen entered, so its effect carries no requirements. A successful back()
always lands on a frame below — an only frame has no screen below it and is
ScreenRootBackError — so the success type never includes undefined.
What a handle's
backreturns and may fail with: the framework's own method. Like every member of a handle it runs with the services held when the screen entered, so its effect carries no requirements. A successfulback()always lands on a frame below — an only frame has no screen below it and isScreenRootBackError— so the success type never includesundefined.