Those mesh diagrams you see are just templates that are used for creating and placing textures on the right spot, they are actually created from the mapping that is applied when the mesh is created in the modeling application. Yes, the CR2 files are just text files, but huge ones - 8000 pages or so, often, so it is helpful to use a utility to work on 'em. I also should add that this whole making clothing thing gets really complicted really quick, it is not something you pick up in a couple of days, or even a couple of weeks.