Changelog update for grouped CMS buttons

docs/en/changelogs/3.1.0.md

@@ -4,6 +4,48 @@
 
 ## Upgrading
 
+### Grouped CMS Buttons
+
+The CMS buttons are now grouped, in order to hide minor actions by default and declutter the interface.
+This required changing the form field structure from a simple `FieldList`
+to a `FieldList` which contains a `CompositeField` for all "major actions",
+and a `TabSet` with a single tab for all "minor actions".
+If you have previously added, removed or altered built-in CMS actions in any way,
+you'll need to adjust your code.
+
+	:::php
+	class MyPage extends Page {
+		function getCMSActions() {
+			$actions = parent::getCMSActions();
+
+			// Inserting a new toplevel action (old)
+			$actions->push(new FormAction('MyAction')); 
+
+			// Inserting a new toplevel action (new)
+			$actions->insertAfter(new FormAction('MyAction'), 'MajorActions');
+
+			// Removing an action, both toplevel and nested (no change required)
+			$actions->removeByName('action_unpublish'); 
+
+			// Inserting a new minor action (new)
+			$actions->addFieldToTab(
+				'Root.ActionMenus.MoreOptions',
+				new FormAction('MyMinorAction')
+			);
+
+			// Finding a toplevel action (no change required)
+			$match = $actions->dataFieldByName('action_save');
+
+			// Finding a nested action (new)
+			$match = $actions->fieldByName('ActionMenus.MoreOptions')
+				->fieldByName('action_MyMinorAction'); 
+
+			return $actions;
+		}
+	}
+
+### Other
+
  * `TableListField`, `ComplexTableField`, `TableField`, `HasOneComplexTableField`, `HasManyComplexTableField` and `ManyManyComplexTableField` have been removed from the core and placed into a module called "legacytablefields" located at https://github.com/silverstripe-labs/legacytablefields
  * `prototype.js` and `behaviour.js` have been removed from the core, they are no longer used. If you have custom code relying on these two libraries, please update your code to include the files yourself
  * `Object::has_extension()` and `Object::add_extension()` deprecated in favour of using late static binding, please use `{class}::has_extension()` and `{class}::add_extension()` instead, where {class} is the class name of your DataObject class.
@@ -45,4 +87,4 @@
    - `DataList#find`
    - `DataList#byIDs`
    - `DataList#reverse`
- * `DataList#dataQuery` has been changed to return a clone of the query, and so can't be used to modify the list's query directly. Use `DataList#alterDataQuery` instead to modify dataQuery in a safe manner.
+ * `DataList#dataQuery` has been changed to return a clone of the query, and so can't be used to modify the list's query directly. Use `DataList#alterDataQuery` instead to modify dataQuery in a safe manner.