Issue #3464894 by grimreaper, pdureau: Drag & drop support in layout builder

modules/ui_patterns_layouts/src/Element/ComponentAlterer.php

@@ -39,8 +39,15 @@ class ComponentAlterer implements TrustedCallbackInterface {
       foreach (Element::children($element[$region_id]) as $block_id) {
         $element["#slots"][$region_id][$block_id] = $element[$region_id][$block_id];
       }
-      if (isset($element[$region_id]['#attributes'])) {
+      if (isset($element[$region_id]['#attributes']) && isset($element['#slots'][$region_id])) {
         $element['#region_attributes'][$region_id] = new Attribute($element[$region_id]['#attributes']);
+        // Support for drag&drop and other attributes manipulation.
+        $element['#slots'][$region_id] = [
+          '#type' => 'html_tag',
+          '#tag' => 'div',
+          '#attributes' => $element[$region_id]['#attributes'],
+          'content' => $element['#slots'][$region_id],
+        ];
       }
       unset($element[$region_id]);
     }