I've just bought Professional Wordpress from Hoepli. This is an interesting book about the Wordpress development that I really missed. Since my web agency likes Wordpress, I think it's time to start using it more deeply. I have to say that my global knowledge on Wordpress is somewhat limited, because I did not dig into more details than just configuring a plugin or simply creating and styling themes. What I need is basically a detailed overview of all the inner components that make Wordpress working as it is so that I can easily perform some customizations without wasting my time on searching for a tip or a tutorial on Google. The description of the product provided by Amazon says that this book is:
An in-depth look at the internals of the WordPress system. As the most popular blogging and content management platform available today, WordPress is a powerful tool. This exciting book goes beyond the basics and delves into the heart of the WordPress system, offering overviews of the functional aspects of WordPress as well as plug-in and theme development.
Just what I needed.