What are some recommended PHP literature for someone with intermediate knowledge in web development?

Issue: Someone with intermediate knowledge in web development may want to deepen their understanding of PHP by reading literature that covers more advanced topics and techniques. Recommended PHP literature for someone with intermediate knowledge in web development include "PHP Objects, Patterns, and Practice" by Matt Zandstra, "Modern PHP: New Features and Good Practices" by Josh Lockhart, and "PHP Advanced and Object-Oriented Programming" by Larry Ullman. Code snippet: N/A