Part I is a deep explanation of what descriptors are, how they work, and how they’re used. It gives enough information that you should be able to look at any descriptor and understand how it works and why it works that way, assuming the writer of the code made the code legible enough.

Creating your own descriptors isn’t difficult once you have the information from Part I, but little to no guidance is given to help with it. Instead, Part II covers that with a bunch of options for creating new descriptors, as well as tips for avoiding common mistakes.