diff -r 000000000000 -r 6474c204b198 editor/libeditor/base/InsertTextTxn.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/editor/libeditor/base/InsertTextTxn.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,149 @@
+/* -*- 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/. */
+
+#include <stdio.h>                      // for printf
+
+#include "InsertTextTxn.h"
+#include "nsAString.h"
+#include "nsDebug.h"                    // for NS_ASSERTION, etc
+#include "nsError.h"                    // for NS_OK, etc
+#include "nsIDOMCharacterData.h"        // for nsIDOMCharacterData
+#include "nsIEditor.h"                  // for nsIEditor
+#include "nsISelection.h"               // for nsISelection
+#include "nsISupportsUtils.h"           // for NS_ADDREF_THIS, NS_RELEASE
+#include "nsITransaction.h"             // for nsITransaction
+
+InsertTextTxn::InsertTextTxn()
+  : EditTxn()
+{
+}
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(InsertTextTxn, EditTxn,
+                                   mElement)
+
+NS_IMPL_ADDREF_INHERITED(InsertTextTxn, EditTxn)
+NS_IMPL_RELEASE_INHERITED(InsertTextTxn, EditTxn)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(InsertTextTxn)
+  if (aIID.Equals(InsertTextTxn::GetCID())) {
+    *aInstancePtr = (void*)(InsertTextTxn*)this;
+    NS_ADDREF_THIS();
+    return NS_OK;
+  } else
+NS_INTERFACE_MAP_END_INHERITING(EditTxn)
+
+NS_IMETHODIMP InsertTextTxn::Init(nsIDOMCharacterData *aElement,
+                                  uint32_t             aOffset,
+                                  const nsAString     &aStringToInsert,
+                                  nsIEditor           *aEditor)
+{
+#if 0
+      nsAutoString text;
+      aElement->GetData(text);
+      printf("InsertTextTxn: Offset to insert at = %d. Text of the node to insert into:\n", aOffset);
+      wprintf(text.get());
+      printf("\n");
+#endif
+
+  NS_ASSERTION(aElement && aEditor, "bad args");
+  NS_ENSURE_TRUE(aElement && aEditor, NS_ERROR_NULL_POINTER);
+
+  mElement = do_QueryInterface(aElement);
+  mOffset = aOffset;
+  mStringToInsert = aStringToInsert;
+  mEditor = aEditor;
+  return NS_OK;
+}
+
+NS_IMETHODIMP InsertTextTxn::DoTransaction(void)
+{
+  NS_ASSERTION(mElement && mEditor, "bad state");
+  if (!mElement || !mEditor) { return NS_ERROR_NOT_INITIALIZED; }
+
+  nsresult result = mElement->InsertData(mOffset, mStringToInsert);
+  NS_ENSURE_SUCCESS(result, result);
+
+  // only set selection to insertion point if editor gives permission
+  bool bAdjustSelection;
+  mEditor->ShouldTxnSetSelection(&bAdjustSelection);
+  if (bAdjustSelection)
+  {
+    nsCOMPtr<nsISelection> selection;
+    result = mEditor->GetSelection(getter_AddRefs(selection));
+    NS_ENSURE_SUCCESS(result, result);
+    NS_ENSURE_TRUE(selection, NS_ERROR_NULL_POINTER);
+    result = selection->Collapse(mElement, mOffset+mStringToInsert.Length());
+    NS_ASSERTION((NS_SUCCEEDED(result)), "selection could not be collapsed after insert.");
+  }
+  else
+  {
+    // do nothing - dom range gravity will adjust selection
+  }
+
+  return result;
+}
+
+NS_IMETHODIMP InsertTextTxn::UndoTransaction(void)
+{
+  NS_ASSERTION(mElement && mEditor, "bad state");
+  if (!mElement || !mEditor) { return NS_ERROR_NOT_INITIALIZED; }
+
+  uint32_t length = mStringToInsert.Length();
+  return mElement->DeleteData(mOffset, length);
+}
+
+NS_IMETHODIMP InsertTextTxn::Merge(nsITransaction *aTransaction, bool *aDidMerge)
+{
+  // set out param default value
+  if (aDidMerge)
+    *aDidMerge = false;
+  nsresult result = NS_OK;
+  if (aDidMerge && aTransaction)
+  {
+    // if aTransaction is a InsertTextTxn, and if the selection hasn't changed, 
+    // then absorb it
+    InsertTextTxn *otherInsTxn = nullptr;
+    aTransaction->QueryInterface(InsertTextTxn::GetCID(), (void **)&otherInsTxn);
+    if (otherInsTxn)
+    {
+      if (IsSequentialInsert(otherInsTxn))
+      {
+        nsAutoString otherData;
+        otherInsTxn->GetData(otherData);
+        mStringToInsert += otherData;
+        *aDidMerge = true;
+      }
+      NS_RELEASE(otherInsTxn);
+    }
+  }
+  return result;
+}
+
+NS_IMETHODIMP InsertTextTxn::GetTxnDescription(nsAString& aString)
+{
+  aString.AssignLiteral("InsertTextTxn: ");
+  aString += mStringToInsert;
+  return NS_OK;
+}
+
+/* ============ protected methods ================== */
+
+NS_IMETHODIMP InsertTextTxn::GetData(nsString& aResult)
+{
+  aResult = mStringToInsert;
+  return NS_OK;
+}
+
+bool InsertTextTxn::IsSequentialInsert(InsertTextTxn *aOtherTxn)
+{
+  NS_ASSERTION(aOtherTxn, "null param");
+  if (aOtherTxn && aOtherTxn->mElement == mElement)
+  {
+    // here, we need to compare offsets.
+    int32_t length = mStringToInsert.Length();
+    if (aOtherTxn->mOffset == (mOffset + length))
+      return true;
+  }
+  return false;
+}