I have changed the code to return true when we have handled/filtered an event. Reason being that the spec explicitly says to do that to prevent any other code also handling the event.
In your reimplementation of this function, if you want to filter the event out, i.e. stop it being handled further, return true; otherwise return false.
There used to be a problem where folders where triggered when the first letter of their name was typed which I believed was because the event was handled by some other code, and that it was fixed by returning true. I can't replicate the incorrect behaviour with 42858f0e though so it's possible I was mistaken.