WordPress Customizer is a relatively recent addition to the WordPress ecosystem. In short, it's a framework meant for live-previewing any changes that the user makes to their website. The Customizer's interface allows for the modification of various aspects of a theme's and website's appearance, starting from the name of the site, the tagline, all the way to the colors used, layouts, widgets, menus, and more. We talked about the Customizer from the user's point of view back in Chapter 8, Customizing Your Website Appearance/Design.
Now, from a developer's perspective, when you're building your WordPress theme, there are a couple of things that you should do in order to make it compatible with the Customizer. Luckily, the starter theme that we're using in this chapter as the foundation...