This is a recipe book, a book that will tell you what works in typography and what you should do with letters.
If you are familiar with the world of design, have studied at a school, or collaborate with designers on a regular basis, you will know that many of the teachers you have had, and many of the professionals in this field, are against a system that would tell you "what you must and must not do", like the system you hold in your hands. They will probably tell you that it is anti-pedagogical or conservative. They will say that in design you always have to try to break the rules, that the great designers are the ones who did just that. And they are right. But it is also true that typography is that important part of graphic design in which it is so difficult to define criteria. It is a specialty that everyone says they love and respect but then nobody, from what I know, is too sure about it.