Héctor A:
> As far as I see when using multiple cursors entering a char causes multiple char added notifications, doesn't it?
No. There is a single notification of the character, not one for each selection.
> I would say it makes sense, however my main concern is related to what to do in this case? The notification doesn't tell where the addition happened.
Use the SCN_MODIFIED notification when you want to determine where characters are added.
Neil