Recently I saw a post on LinkedIn about a recruiter that is primarily working on the PHP Market asking for input on what are important factors to know about PHP. If you want to learn PHP, you look for existing professionals so that you can learn what they do.
This post is me attempting something I never did before: explain PHP to a recruiter from my point of view.
For a senior engineer with 12 years of experience today, the universe of PHP largely revolves around PHP 4, 5, 7 and 8.
Given it's history of vanilla / each company it's own standard background, PHP had an important innovation with the rise of the PSR Working Ground (PHP Standards Recommendations).