Some speculation about making opaque root finding cheaper.

third_party/WebKit/Source/core/dom/Node.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004-2011, 2014 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 315 matching lines @@
 
   // Returns nullptr, a child of ShadowRoot, or a legacy shadow root.
   Node* nonBoundaryShadowTreeRootNode();
 
   // Node's parent, shadow tree host.
   ContainerNode* parentOrShadowHostNode() const;
   Element* parentOrShadowHostElement() const;
   void setParentOrShadowHostNode(ContainerNode*);
 
   // Knows about all kinds of hosts.
-  ContainerNode* parentOrShadowHostOrTemplateHostNode() const;
+  ContainerNode* parentOrShadowHostOrTemplateHostNode() const {
+    if (UNLIKELY(isDocumentFragment() && !isShadowRoot()))
+      return parentOrShadowHostOrTemplateHostNodeForDocumentFragment();
+    return parentOrShadowHostNode();
+  }
+  ContainerNode* parentOrShadowHostOrTemplateHostNodeForDocumentFragment()
+      const;
 
   // Returns the parent node, but nullptr if the parent node is a ShadowRoot.
   ContainerNode* nonShadowBoundaryParentNode() const;
 
   // Returns the enclosing event parent Element (or self) that, when clicked,
   // would trigger a navigation.
   Element* enclosingLinkEventParentOrSelf() const;
 
   // These low-level calls give the caller responsibility for maintaining the
   // integrity of the tree.
@@ skipping 678 matching lines @@
 }  // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showNode(const blink::Node*);
 void showTree(const blink::Node*);
 void showNodePath(const blink::Node*);
 #endif
 
 #endif  // Node_h