After some time I realised that inventory actions are room sensitive: when I display a message on look action on certain item in my custom inventory, it displays message by message number in current room. Is it possible to make it global, or do I have to make separate messages for each room?
Go to the "Global Messages" section of the editor. Click on a slot, and type away. Then use that slot number in the messages window. :=
Alternatively you can also run script and get this:
Display("Your message goes here.");
It' even better with global values, which mean s you can change them. ;D