For some time, I have been learning WordPress so that I could redo our church's web site to move it to WordPress from another CMS (Content Management System). Since I wanted the web site to look pretty much the same as it did under the other CMS, I could not find a WordPress theme that would work, so I built one myself, following a very useful web site article.
One positive thing about WordPress is its plugins. One negative thing about WordPress is its plugins.
On the one hand, you can find a plugin to do almost (but not quite) anything for your WordPress site. On the other hand, you have to use plugins to change or add behavior that ought to be built into WordPress.
Also, I have on many occasions been looking for a plugin to accomplish something I needed, and while I often found one (more usually, many), they so often didn't fill the bill to my satisfaction. They might have omitted a feature I needed, or perhaps were too complicated and contained more than I needed.
So, I wanted to find out how to write my own plugin(s) to provide just what I wanted. Thus, I was lead this book. It's probably the best book going on WordPress plugins, and provides very useful information and help on how to write your own plugin. Unfortunately, it left me wanting more. For example, I wanted to learn how to write a plugin to incorporate various features of JQuery, but the book doesn't talk about that.
So, I only gave it 4 stars, rather than 5. Now, to try to learn more about plugins some other way...