Can you recall where it's documented, or where I can find some info / examples about it ?

No, it's just one of the first things you learn when using the API from (pre-.NET) VB. In fact, I often use the API declarations for VB as the starting point to convert them to Win32::API. You can do the same, just Google for inurl:Win32API.txt to find a copy.

I've been Googling around for it on the net yesterday, but I haven't found it back in one sentence, at all. Sorry about that.

According to the Win32::API docs, 'N' is not the only integer prototype, there's also 'N'

Eh? I'm sure you mean 'I', and AFAIK that does mean the same as 'N'.