It's everything you need to know, from the bottom up.
Written by Mike Myers
Let me first explain a little about myself. I wrote my first program in 1982 on a System/34 (RPG II). Two years later, I was on the System/38 (RPG III), and soon after, the AS/400 (RPG IV, etc.). So, yes, I am an old green-screen developer—working hard, I might add, to update my skill set using Rational Developer for i for SOA Construction (RDi SOA).
I found Joe's book very useful in introducing me to the key concepts of EGL—namely widgets, library functions, reusable components, and completely encapsulated shared projects.