The following subchapter isn't one you have to go through step by step, it's rather a collection of small snippets that you can use to improve your concrete5 theme or block. The code snippets won't have any purpose in the upcoming chapters—you can implement them if you like, but you don't have to.
By default, concrete5 sets a bunch of constants that you can use when you create a theme but also a block or any other type of add-on. A lot of these constants are used internally and don't have any use for you when building themes or add-ons, but some are helpful and the rest give you at least an impression about a few internal workings of concrete5. There are also lots of functions to check the state of the current page, get information about the user, and much more.
While the basic template we've created works well for most situations, there are several things you can do within a template and not only in the user interface. The code lines aren't real life examples...