I think memorizing the manual is the least important thing when it comes to judging skill level. The most important thing is given ANY project being able to stand-up an environment to work on it and resolve business problems with LITTLE guidance in terms of PHP questions. For example there seem to be a lot of questions lately on standing up basic environments to get projects running a local instance. Those people can not be considered experts and could probably hardly be considered intermediate in most cases. Knowing the language is useless without practical application in real world set-ups with continuous integration set-ups and basic server admin architecture to stand-up an environment or at the very least knowing how to google for the answers to the right questions and resolve them ones self. Though now I guess I’m heading more towards genera; web development expertise which isn’t really “php” but I don’t think being an expert in"php" isn’t without being an expert in building websites. Similar to being able to play an instrument but unable to read sheet music.