This is the third installment in a series presenting configuration management work that comes out of the Drutopia initiative.

• In part 1 of this series, Configuration Providers, we introduced the problem of managing shared configuration in Drupal, starting with how to determine what configuration is available.
• In part 2, Configuration Snapshots, we covered creating snapshots of configuration to facilitate comparison of different configuration states.
• In this installment, we'll look at another key issue when updating shared configuration: how to handle customizations.

To help clarify the problem, take this scenario:

• You install a site from a Drupal distribution.
• One of the pieces of configuration that distribution provides is an event content type.
• You edit the content type to tweak the help text that appears when a user creates a new piece of content.
• Now a new release of the distribution is available.

You want to update to the new version and get any updates it provides, including any changes that were made to the event content type. But - and here's the tricky part - when you update, you don't want to lose the customization you made to event the content type's help text.