diff -r 000000000000 -r 6474c204b198 editor/libeditor/base/JoinElementTxn.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/editor/libeditor/base/JoinElementTxn.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,63 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef JoinElementTxn_h__
+#define JoinElementTxn_h__
+
+#include "EditTxn.h"                    // for EditTxn, NS_DECL_EDITTXN
+#include "nsCOMPtr.h"                   // for nsCOMPtr
+#include "nsCycleCollectionParticipant.h"
+#include "nsID.h"                       // for REFNSIID
+#include "nsIDOMNode.h"                 // for nsIDOMNode
+#include "nscore.h"                     // for NS_IMETHOD
+
+class nsEditor;
+
+/**
+ * A transaction that joins two elements E1 (left node) and E2 (right node)
+ * into a single node E.  
+ * The children of E are the children of E1 followed by the children of E2.
+ * After DoTransaction() and RedoTransaction(), E1 is removed from the content
+ * tree and E2 remains.
+ */
+class JoinElementTxn : public EditTxn
+{
+public:
+  /** initialize the transaction
+    * @param aEditor    the provider of core editing operations
+    * @param aLeftNode  the first of two nodes to join
+    * @param aRightNode the second of two nodes to join
+    */
+  NS_IMETHOD Init(nsEditor   *aEditor,
+                  nsIDOMNode *aLeftNode,
+                  nsIDOMNode *aRightNode);
+
+  JoinElementTxn();
+
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(JoinElementTxn, EditTxn)
+  NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr);
+
+  NS_DECL_EDITTXN
+
+protected:
+  
+  /** the elements to operate upon.  
+    * After the merge, mRightNode remains and mLeftNode is removed from the content tree.
+    */
+  nsCOMPtr<nsIDOMNode> mLeftNode;
+  nsCOMPtr<nsIDOMNode> mRightNode;
+
+  /** the offset into mNode where the children of mElement are split (for undo).<BR>
+    * mOffset is the index of the first child in the right node. 
+    * -1 means the left node had no children.
+    */
+  uint32_t  mOffset;
+
+  /** the parent node containing mLeftNode and mRightNode */
+  nsCOMPtr<nsIDOMNode> mParent;
+  nsEditor*  mEditor;
+};
+
+#endif