AFDKO and font variants in features files



My questions would probably appear quite obvious to you, but I have failed to find any answer around Google or in the AFDKO specs (perhaps because I'm not using the good keywords?)

I'm using a spanish OTF font with (Lua)Latex which shows some minor problems for my language (french, namely) and, for example, comes with very tight-kerned apostrophe. I use a .fea file in Latex to add some space around it, and fix some exotic glyph combinations.