Starting with 5240116f3c we only support
GHC versions 8.4.4 and up (more precisely, the GHC version associated
with stackage lts-12 and up). The imports in question are now in
Prelude and need not be imported explicitly.
All False short-cuts the default behavior for the event, which leads to a non-functioning window manager. Returning mempty ensures that the default action is still executed,
Run a ManageHook from handleEventHook when a window property changes.
You would use this to match e.g. browser windows whose title is not
"final" until after the on-load hooks of the loaded document complete.
