As far as I know, you can add affixes to just about any item in the game (wings, flag, potions, dyes, etc), but those affixes are only for show. They do not provide the actual skill in game.
I do not have an answer regarding GAIN X. I have seen it quite a few times and I did know where it was in the editor, but I do not know without looking and I am not in front of the right computer for that. It may just have been an affix tied to a certain ring or other piece of equipment. I suspect that the GAIN X does not actually do anything either. For example, there are a lot of test rings that you can make that do nothing or that are not implemented in the game yet. One thing is for sure, just because it is available on the editor does not mean it automatically provides an actual benefit in game.
If you find the GAIN X test it in game to see how your stats change and let us all know what you find out.
I do not have an answer regarding GAIN X. I have seen it quite a few times and I did know where it was in the editor, but I do not know without looking and I am not in front of the right computer for that. It may just have been an affix tied to a certain ring or other piece of equipment. I suspect that the GAIN X does not actually do anything either. For example, there are a lot of test rings that you can make that do nothing or that are not implemented in the game yet. One thing is for sure, just because it is available on the editor does not mean it automatically provides an actual benefit in game.
If you find the GAIN X test it in game to see how your stats change and let us all know what you find out.