I completely agree, most people I've ever encountered asking "What to learn next" don't really understand what they think they know. There are 100 different dir

I completely agree, most people I've ever encountered asking "What to learn next" don't really understand what they think they know. There are 100 different directions you can go from if you actually had a decent understanding of php/html/css; exploring the PHP source code, learning more about the network protocols that http/https requests operate on top of, web application security and security in general, browser implementation of css rendering/javascript engines/sandboxing, all of these things are natural extensions of web development, and are really just the tip of the iceberg.