We have been examining hooks since the first chapter of this book. Now we are going to take an in-depth look at how a module can implement its own hook.

In this section, we will invoke a custom hook, implement that hook in other modules, and look at the mechanics of using hooks.

The goal of defining this hook is to make it possible for other modules to earmark content for inclusion in a site news message. This gives the module developers the ability to specify what content should be included in a report, and how it should appear.

We will start out by backtracking. Let's take another look at the hook invocation from the last section.

$content = module_invoke_all('sitenews');