feat: check if element is in a shadowroot.

application/source/dom/updater.mjs

@@ -543,6 +543,15 @@ function internalTemplateLookUp(container, key, ref, path) {
         }
     }
 
+    const rootNode = container.getRootNode();
+    if (rootNode instanceof ShadowRoot) {
+        templateID = rootNode.host.getAttribute(ATTRIBUTE_UPDATER_INSERT_TEMPLATE_ID);
+        template = findDocumentTemplate(templateID, container);
+        if (template instanceof HTMLTemplateElement) {
+            return template;
+        }
+    }
+
     return findDocumentTemplate(templateID, container);
 }