The scripter is playing the current cutscene,which is
executed in a coroutine (as some instructions need
synchronization with the C part of the game, i.e. when
saying things the player must hit a button to
continue):
1 - NPC1 says "Hello"
2 - NPC1 moves forward 5 steps
3 - NPC1 turns to NPC2
4 - NPC1 says "It's been a long time"
5 - NPC2 says "..."
imagine the creator sees the script reproduced in the
tool, and once it reaches and executes #4, he decides
that he wants to see again from #2 (cutscenes can have
100s of lines, so it'd be useful to avoid 40 seconds
of cutscene)
The first step would be "rewinding" the execution to
instruction #2 so that he can see the process again.
I'd like to offer the user a kind of "time bar" so
that he can rewind to any previous position. Fast
forward is easier (just run through the script).