gogtrial34987: GOG has released
official mods (see
reddit announcement, as I don't see a forum thread for it yet), which have a new relation type, "modifiesGames". I'm swamped the next few days, so it might take me until Thursday before I can correctly handle these. Until then I'll treat them as expansions, although it'll require manual action to assign them as such, so when new ones appear, they'll initially show as full games. (I'm somewhat baffled by them not having the requires relation.)
I think it's questionable whether they should be treated as expansions, given that GOG treats them essentially as standalone games when it adds them to one's library.
The three that I have (HOMM3 Horn of the Abyss, VTMB Unofficial Patch, Chronicles of Myrtana Archolos) each have their own separate library entry, and the last one even has a DLC of its own, which is most certainly not a DLC of Gothic 2.
Moreover, you can play any of these "mods" without installing the base game.
P.S. The name mod is very confusing. These are NOT mods, but rather modded standalone games.
P.P.S. I don't see why, for example, Archolos would be considered an expansion of Gothic 2 (they have little in common), while Spellforce 3 Soul Harvest is not considered an expansion of Spellforce 3 (which it clearly is).