The cause of a departure a beforeLeave runs for — the transition's via (the edge's source
and ordinal skip) for a tab switch or a screen entering over the frame, or a cause of its own
where the departure is not a navigation source: 'back' for a back (the NavigateBack verb),
'close' for a screen closed by its own action (closeScreen) and 'interruption' for a frame
an interruption with no navigation source (a challenge step) covers.
The cause of a departure a
beforeLeaveruns for — the transition'svia(the edge's source and ordinal skip) for a tab switch or a screen entering over the frame, or a cause of its own where the departure is not a navigation source:'back'for aback(theNavigateBackverb),'close'for a screen closed by its own action (closeScreen) and'interruption'for a frame an interruption with no navigation source (a challenge step) covers.