Welcome to our free course on object-oriented PHP (OOPHP) for WordPress. This course explains the following:

Far too often, a developer comes in to “modernize” a site—and ends up wrecking a thriving online business by ruining its SEO.

A lot of my work in WordPress is tacit knowledge: general know-how that I take for granted, and that it doesn’t even occur to me I have. The problem with tacit knowledge in teaching is that other people might miss important things that it wouldn’t even occur to you to teach because it feels “too basic.”

One of the most maligned features of WordPress is the rampant use of “PHP global variables.” There are huge decades-long discussions in software development circles about why heavy reliance on globally scoped variables is a bad design decision, but that debate is beyond the scope of what I want to cover here. (If that topic is interesting to you, the C2 Wiki article on it is a good starting point for understanding the arguments.) What I want to explain is instead what variable scope means, and why and how global variables are used in WordPress.