Precisely. What CSS-Tricks calls a guide is actually almost entirely a reference. It makes a tolerable reference if you already know what you’re looking for. It’s a poor reference if you don’t know what you’re looking for because it’s insufficiently structured and takes waaaaay too much scrolling to explore. (It used to be more manageable—it used to be more a guide. It has been allowed to grow far beyond a healthy point.) And it’s atrocious as a guide.

And, typically, there are several levels of textbook. e.g. high school, then freshman physics, undergrad electrodynamics, then Jackson, then specialist references.

My point is you go over the subject completely several times, at increasing levels of sophistication.