When going to a mod's page on forge and clicking "File" you can download different files of the mod for different versions of minecraft but there's a section on the different files that say "type". So far I've seen 3 different types of files, A (grey box with an A inside), B (Blue box with a B inside) and R (Green box with an R inside). my problem is I don't know what they mean. (I've added a picture for reference)