We are all lucky to live in a world where the open source movement gives us such incredible access to knowledge and hence capabilities. Personally, I owe a huge debt to the WordPress, Drupal, and Joomla communities.
While the things that I know about these systems were not acquired in a classroom, it would be dishonest to say that I am self-taught. Like most of us, I consume countless books, articles, and postings and distill that information down into my own procedures and techniques. I have absorbed every source that I could get my hands on, and condensed that source material down into my own set of processes and techniques.
I am in the process of moving my WordPress development notes over the the support site for the meetup I run, please take a look here: https://webprosmeetup.org/category/knowledge/
Enjoy!