`registration` Registration Decorator does not appear to be explained. There is no "DI customization article"

In DI Basics/Explicit Configuration:

> registration(registration: Registration) - In addition to the built-in singleton and transient registrations, you can create your own and associate it with a class. We'll discuss this in more detail in the DI customization article.

I can't find a "DI customization article", thus `registration` doesn't not appear to be explained.

Start in the DI Basics/Explicit Configuration section and search the documentation for the referenced “DI customization article.” Determine whether the article is missing or the reference is outdated. Done means the registration decorator is explained and the documentation points readers to the relevant explanation.

Written by the indexing model from the issue text.