I think I've seen it somewhere a few years back, but couldn't find a mention anywhere.
I'm developing an IDAPython plugin and I'd like to embed IDB-specific information inside IDBs. Obviously, I could write that data into another file but embedding it into IDB files will really suit my needs.
The data itself is quite simple and small, I could do with few tens (hundred max) of bytes. I can go one binary blob or free-text/json that I manually manage.
I thought about adding a section of my own, but that's a bit too hacky and IDA instances without my plugin will show it to the user.