Are there any books, websites or lectures that explain the built-in WordPress classes? I would really like to learn how WordPress works internally.
I've dug up the core files on trac and even went through the class reference on codex but yet I find it difficult to learn this way.
I know this is not a place to be asking for resources but everywhere I search the results are theme/plugin tutorials. I really want to understand the internal working of WordPress, can anyone give me pointers to go ahead with this? My PHP skills are just above intermediate