DOC Protected extension hook implementations in changelog

en/08_Changelogs/6.0.0.md

@@ -11,6 +11,7 @@ title: 6.0.0 (unreleased)
   - [Other new features](#other-new-features)
 - [Bug fixes](#bug-fixes)
 - [API changes](#api-changes)
+  - [Most extension hook methods are now protected](#hooks-protected)
   - [General changes](#api-general)
 
 ## Features and enhancements
@@ -38,6 +39,10 @@ This release includes a number of bug fixes to improve a broad range of areas. C
 
 ## API changes
 
+### Most extension hook methods are now protected
+
+Core implementations of most extension hooks such as `updateCMSFields()` now have protected visibility. Formally they had public visibility which meant they could be called directly which was not how they were intended to be used. Extension hook implementations are still able to be declared public in project code, though it is recommended that all extension hook methods are declared protected in project code to follow best practice.
+
 ### General changes {#api-general}
 
 - [`DataObject::write()`](api:SilverStripe\ORM\DataObject::write()) has a new boolean `$skipValidation` parameter. This can be useful for scenarios where you want to automatically create a new record with no data initially without restricting how developers can set up their validation rules.