In the previous chapters, we learned about the fundamental principles of Drupal 8's Configuration Management, and took a look at the Configuration Management API. So we now know how to work with configuration objects and how to read and write individual configuration.

However, how does Drupal validate data within a site's configuration? We probably need a setting to accept integer values or a URI. Or we would like to enforce fixed structure in our configuration data. This is exactly where schema files come into play.

This chapter will tell you about schema files and how Drupal uses them for Configuration Management. We will learn about the structure of schema files used by Drupal and how you can write your own schema for custom configuration.