La réponse du big chief! ;)
Et il y a peu de chance que cela change dans les mois à venir! ;)

Hi Pilou , MoI is designed to only have one file open per session. One reason for that is so the files are independent and something like a program crash or modal UI dialog will only affect that one file and not all of them.

On Windows it is most common to use multiple program sessions to handle multiple files. On Mac it is not common so this is an area where the MoI Mac version behaves a little differently than many other Mac apps.

> So working on several files oblige to open the same number of Moi's sessions ?
Yes, that is correct. The MoI Mac version will open a new session for you by using the “New Window” menu item on the Top menu bar.

Voilà un mystère éclairci !