diff --git a/editor/libeditor/base/nsEditor.cpp b/editor/libeditor/base/nsEditor.cpp
index 0f8f08ec300..24ede4e6567 100644
--- a/editor/libeditor/base/nsEditor.cpp
+++ b/editor/libeditor/base/nsEditor.cpp
@@ -3839,23 +3839,7 @@ nsEditor::TagCanContain(const nsAString &aParentTag, nsIDOMNode* aChild)
 PRBool 
 nsEditor::TagCanContainTag(const nsAString &aParentTag, const nsAString &aChildTag)
 {
-  // if we don't have a dtd then assume we can insert whatever want
-  if (!mDTD) return PR_TRUE;
-
-  PRInt32 childTagEnum;
-  // XXX Should this handle #cdata-section too?
-  if (aChildTag.EqualsLiteral("#text")) {
-    childTagEnum = eHTMLTag_text;
-  }
-  else {
-    childTagEnum = sParserService->HTMLStringTagToId(aChildTag);
-  }
-
-  PRInt32 parentTagEnum = sParserService->HTMLStringTagToId(aParentTag);
-  NS_ASSERTION(parentTagEnum < NS_HTML_TAG_MAX,
-               "Fix the caller, this type of node can never contain children.");
-
-  return mDTD->CanContain(parentTagEnum, childTagEnum);
+  return PR_TRUE;
 }
 
 PRBool 
@@ -3896,13 +3880,7 @@ nsEditor::IsDescendantOfBody(nsIDOMNode *inNode)
 PRBool 
 nsEditor::IsContainer(nsIDOMNode *aNode)
 {
-  if (!aNode) return PR_FALSE;
-  nsAutoString stringTag;
-  nsresult res = aNode->GetNodeName(stringTag);
-  if (NS_FAILED(res)) return PR_FALSE;
-  PRInt32 tagEnum = sParserService->HTMLStringTagToId(stringTag);
-
-  return mDTD->IsContainer(tagEnum);
+  return aNode ? PR_TRUE : PR_FALSE;
 }
 
 PRBool
diff --git a/editor/libeditor/base/nsEditor.h b/editor/libeditor/base/nsEditor.h
index e4af6493db8..b05d6fb66f2 100644
--- a/editor/libeditor/base/nsEditor.h
+++ b/editor/libeditor/base/nsEditor.h
@@ -56,7 +56,6 @@
 #include "nsIComponentManager.h"
 #include "nsISupportsArray.h"
 #include "nsICSSStyleSheet.h"
-#include "nsIDTD.h"
 #include "nsIDOMElement.h"
 #include "nsSelectionState.h"
 #include "nsIEditorSpellCheck.h"
@@ -489,7 +488,7 @@ public:
   PRBool IsDescendantOfBody(nsIDOMNode *inNode);
 
   /** returns PR_TRUE if aNode is a container */
-  PRBool IsContainer(nsIDOMNode *aNode);
+  virtual PRBool IsContainer(nsIDOMNode *aNode);
 
   /** returns PR_TRUE if aNode is an editable node */
   PRBool IsEditable(nsIDOMNode *aNode);
@@ -626,7 +625,6 @@ protected:
   // receiver when we get it off anonymous content because during document
   // teardown the anonymous content can get unhooked before we get unhooked.
   nsCOMPtr<nsIDOMEventReceiver> mDOMEventReceiver;
-  nsCOMPtr<nsIDTD> mDTD;
 
   nsString* mPhonetic;
 
diff --git a/editor/libeditor/html/nsHTMLEditUtils.cpp b/editor/libeditor/html/nsHTMLEditUtils.cpp
index f36397cb638..6eb936e37d8 100644
--- a/editor/libeditor/html/nsHTMLEditUtils.cpp
+++ b/editor/libeditor/html/nsHTMLEditUtils.cpp
@@ -47,6 +47,7 @@
 #include "nsIContent.h"
 #include "nsIDOMNodeList.h"
 #include "nsIDOMHTMLAnchorElement.h"
+#include "nsHTMLTags.h"
 
 ///////////////////////////////////////////////////////////////////////////
 //                  
@@ -455,3 +456,313 @@ nsHTMLEditUtils::SupportsAlignAttr(nsIDOMNode * aNode)
       || (nodeAtom == nsEditProperty::h5)
       || (nodeAtom == nsEditProperty::h6);
 }
+
+// We use bitmasks to test containment of elements. Elements are marked to be
+// in certain groups by setting the mGroup member of the nsElementInfo struct
+// to the corresponding GROUP_ values (OR'ed together). Similarly, elements are
+// marked to allow containment of certain groups by setting the
+// mCanContainGroups member of the nsElementInfo struct to the corresponding
+// GROUP_ values (OR'ed together).
+// Testing containment then simply consists of checking whether the
+// mCanContainGroups bitmask of an element and the mGroup bitmask of a
+// potential child overlap.
+
+#define GROUP_NONE             0
+
+// body, head, html
+#define GROUP_TOPLEVEL         (1 << 1)  
+
+// base, isindex, link, meta, script, style, title
+#define GROUP_HEAD_CONTENT     (1 << 2)
+
+// b, big, i, s, small, strike, tt, u
+#define GROUP_FONTSTYLE        (1 << 3)
+
+// abbr, acronym, cite, code, del, dfn, em, ins, kbd, samp, strong, var
+#define GROUP_PHRASE           (1 << 4)
+
+// a, applet, basefont, bdo, br, font, iframe, img, map, object, q, script,
+// span, sub, sup
+#define GROUP_SPECIAL          (1 << 5)
+
+// button, form, input, label, select, textarea
+#define GROUP_FORMCONTROL      (1 << 6)
+
+// address, applet, blockquote, button, center, del, dir, div, dl, fieldset,
+// form, h1, h2, h3, h4, h5, h6, hr, iframe, ins, isindex, map, menu, noframes,
+// noscript, object, ol, p, pre, table, ul
+#define GROUP_BLOCK            (1 << 7)
+
+// frame, frameset
+#define GROUP_FRAME            (1 << 8)
+
+// col, tbody
+#define GROUP_TABLE_CONTENT    (1 << 9)
+
+// tr
+#define GROUP_TBODY_CONTENT    (1 << 10)
+
+// td, th
+#define GROUP_TR_CONTENT       (1 << 11)
+
+// col
+#define GROUP_COLGROUP_CONTENT (1 << 12)
+
+// param
+#define GROUP_OBJECT_CONTENT   (1 << 13)
+
+// li
+#define GROUP_LI               (1 << 14)
+
+// area
+#define GROUP_MAP_CONTENT      (1 << 15)
+
+// optgroup, option
+#define GROUP_SELECT_CONTENT   (1 << 16)
+
+// option
+#define GROUP_OPTGROUP_CONTENT (1 << 17)
+
+// dd, dt
+#define GROUP_DL_CONTENT       (1 << 18)
+
+// p
+#define GROUP_P                (1 << 19)
+
+// text, whitespace, newline, comment
+#define GROUP_LEAF             (1 << 20)
+
+// XXX This is because the editor does sublists illegally. 
+// ol, ul
+#define GROUP_OL_UL            (1 << 21)
+
+#define GROUP_INLINE_ELEMENT \
+  (GROUP_FONTSTYLE | GROUP_PHRASE | GROUP_SPECIAL | GROUP_FORMCONTROL | \
+   GROUP_LEAF)
+
+#define GROUP_FLOW_ELEMENT (GROUP_INLINE_ELEMENT | GROUP_BLOCK)
+
+struct nsElementInfo
+{
+#ifdef DEBUG
+  eHTMLTags mTag;
+#endif
+  PRUint32 mGroup;
+  PRUint32 mCanContainGroups;
+  PRPackedBool mIsContainer;
+  PRPackedBool mCanContainSelf;
+};
+
+#ifdef DEBUG
+#define ELEM(_tag, _isContainer, _canContainSelf, _group, _canContainGroups) \
+  { eHTMLTag_##_tag, _group, _canContainGroups, _isContainer, _canContainSelf }
+#else
+#define ELEM(_tag, _isContainer, _canContainSelf, _group, _canContainGroups) \
+  { _group, _canContainGroups, _isContainer, _canContainSelf }
+#endif
+
+static const nsElementInfo kElements[eHTMLTag_userdefined] = {
+  ELEM(a, PR_TRUE, PR_FALSE, GROUP_SPECIAL, GROUP_INLINE_ELEMENT),
+  ELEM(abbr, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(acronym, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(address, PR_TRUE, PR_TRUE, GROUP_BLOCK,
+       GROUP_INLINE_ELEMENT | GROUP_P),
+  ELEM(applet, PR_TRUE, PR_TRUE, GROUP_SPECIAL | GROUP_BLOCK,
+       GROUP_FLOW_ELEMENT | GROUP_OBJECT_CONTENT),
+  ELEM(area, PR_FALSE, PR_FALSE, GROUP_MAP_CONTENT, GROUP_NONE),
+  ELEM(b, PR_TRUE, PR_TRUE, GROUP_FONTSTYLE, GROUP_INLINE_ELEMENT),
+  ELEM(base, PR_FALSE, PR_FALSE, GROUP_HEAD_CONTENT, GROUP_NONE),
+  ELEM(basefont, PR_FALSE, PR_FALSE, GROUP_SPECIAL, GROUP_NONE),
+  ELEM(bdo, PR_TRUE, PR_TRUE, GROUP_SPECIAL, GROUP_INLINE_ELEMENT),
+  ELEM(bgsound, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(big, PR_TRUE, PR_TRUE, GROUP_FONTSTYLE, GROUP_INLINE_ELEMENT),
+  ELEM(blink, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(blockquote, PR_TRUE, PR_TRUE, GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(body, PR_TRUE, PR_TRUE, GROUP_TOPLEVEL, GROUP_FLOW_ELEMENT),
+  ELEM(br, PR_FALSE, PR_FALSE, GROUP_SPECIAL, GROUP_NONE),
+  ELEM(button, PR_TRUE, PR_TRUE, GROUP_FORMCONTROL | GROUP_BLOCK,
+       GROUP_FLOW_ELEMENT),
+  ELEM(canvas, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(caption, PR_TRUE, PR_TRUE, GROUP_NONE, GROUP_INLINE_ELEMENT),
+  ELEM(center, PR_TRUE, PR_TRUE, GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(cite, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(code, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(col, PR_FALSE, PR_FALSE, GROUP_TABLE_CONTENT | GROUP_COLGROUP_CONTENT,
+       GROUP_NONE),
+  ELEM(colgroup, PR_TRUE, PR_FALSE, GROUP_NONE, GROUP_COLGROUP_CONTENT),
+  ELEM(dd, PR_TRUE, PR_FALSE, GROUP_DL_CONTENT, GROUP_FLOW_ELEMENT),
+  ELEM(del, PR_TRUE, PR_TRUE, GROUP_PHRASE | GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(dfn, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(dir, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_LI),
+  ELEM(div, PR_TRUE, PR_TRUE, GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(dl, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_DL_CONTENT),
+  ELEM(dt, PR_TRUE, PR_TRUE, GROUP_DL_CONTENT, GROUP_INLINE_ELEMENT),
+  ELEM(em, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(embed, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(fieldset, PR_TRUE, PR_TRUE, GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(font, PR_TRUE, PR_TRUE, GROUP_SPECIAL, GROUP_INLINE_ELEMENT),
+  ELEM(form, PR_TRUE, PR_TRUE, GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(frame, PR_FALSE, PR_FALSE, GROUP_FRAME, GROUP_NONE),
+  ELEM(frameset, PR_TRUE, PR_TRUE, GROUP_FRAME, GROUP_FRAME),
+  ELEM(h1, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_INLINE_ELEMENT),
+  ELEM(h2, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_INLINE_ELEMENT),
+  ELEM(h3, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_INLINE_ELEMENT),
+  ELEM(h4, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_INLINE_ELEMENT),
+  ELEM(h5, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_INLINE_ELEMENT),
+  ELEM(h6, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_INLINE_ELEMENT),
+  ELEM(head, PR_TRUE, PR_FALSE, GROUP_TOPLEVEL, GROUP_HEAD_CONTENT),
+  ELEM(hr, PR_FALSE, PR_FALSE, GROUP_BLOCK, GROUP_NONE),
+  ELEM(html, PR_TRUE, PR_FALSE, GROUP_TOPLEVEL, GROUP_TOPLEVEL),
+  ELEM(i, PR_TRUE, PR_TRUE, GROUP_FONTSTYLE, GROUP_INLINE_ELEMENT),
+  ELEM(iframe, PR_TRUE, PR_TRUE, GROUP_SPECIAL | GROUP_BLOCK,
+       GROUP_FLOW_ELEMENT),
+  ELEM(image, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(img, PR_FALSE, PR_FALSE, GROUP_SPECIAL, GROUP_NONE),
+  ELEM(input, PR_FALSE, PR_FALSE, GROUP_FORMCONTROL, GROUP_NONE),
+  ELEM(ins, PR_TRUE, PR_TRUE, GROUP_PHRASE | GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(isindex, PR_FALSE, PR_FALSE, GROUP_BLOCK | GROUP_HEAD_CONTENT,
+       GROUP_NONE),
+  ELEM(kbd, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(keygen, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(label, PR_TRUE, PR_FALSE, GROUP_FORMCONTROL, GROUP_INLINE_ELEMENT),
+  ELEM(legend, PR_TRUE, PR_TRUE, GROUP_NONE, GROUP_INLINE_ELEMENT),
+  ELEM(li, PR_TRUE, PR_FALSE, GROUP_LI, GROUP_FLOW_ELEMENT),
+  ELEM(link, PR_FALSE, PR_FALSE, GROUP_HEAD_CONTENT, GROUP_NONE),
+  ELEM(listing, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(map, PR_TRUE, PR_TRUE, GROUP_SPECIAL, GROUP_BLOCK | GROUP_MAP_CONTENT),
+  ELEM(marquee, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(menu, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_LI),
+  ELEM(meta, PR_FALSE, PR_FALSE, GROUP_HEAD_CONTENT, GROUP_NONE),
+  ELEM(multicol, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(nobr, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(noembed, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(noframes, PR_TRUE, PR_TRUE, GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(noscript, PR_TRUE, PR_TRUE, GROUP_BLOCK, GROUP_FLOW_ELEMENT),
+  ELEM(object, PR_TRUE, PR_TRUE, GROUP_SPECIAL | GROUP_BLOCK,
+       GROUP_FLOW_ELEMENT | GROUP_OBJECT_CONTENT),
+  // XXX Can contain self and ul because editor does sublists illegally.
+  ELEM(ol, PR_TRUE, PR_TRUE, GROUP_BLOCK | GROUP_OL_UL,
+       GROUP_LI | GROUP_OL_UL),
+  ELEM(optgroup, PR_TRUE, PR_FALSE, GROUP_SELECT_CONTENT,
+       GROUP_OPTGROUP_CONTENT),
+  ELEM(option, PR_TRUE, PR_FALSE,
+       GROUP_SELECT_CONTENT | GROUP_OPTGROUP_CONTENT, GROUP_LEAF),
+  ELEM(p, PR_TRUE, PR_FALSE, GROUP_BLOCK | GROUP_P, GROUP_INLINE_ELEMENT),
+  ELEM(param, PR_FALSE, PR_FALSE, GROUP_OBJECT_CONTENT, GROUP_NONE),
+  ELEM(plaintext, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(pre, PR_TRUE, PR_TRUE, GROUP_BLOCK, GROUP_INLINE_ELEMENT),
+  ELEM(q, PR_TRUE, PR_TRUE, GROUP_SPECIAL, GROUP_INLINE_ELEMENT),
+  ELEM(s, PR_TRUE, PR_TRUE, GROUP_FONTSTYLE, GROUP_INLINE_ELEMENT),
+  ELEM(samp, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(script, PR_TRUE, PR_FALSE, GROUP_HEAD_CONTENT | GROUP_SPECIAL,
+       GROUP_LEAF),
+  ELEM(select, PR_TRUE, PR_FALSE, GROUP_FORMCONTROL, GROUP_SELECT_CONTENT),
+  ELEM(server, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(small, PR_TRUE, PR_TRUE, GROUP_FONTSTYLE, GROUP_INLINE_ELEMENT),
+  ELEM(sound, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(spacer, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(span, PR_TRUE, PR_TRUE, GROUP_SPECIAL, GROUP_INLINE_ELEMENT),
+  ELEM(strike, PR_TRUE, PR_TRUE, GROUP_FONTSTYLE, GROUP_INLINE_ELEMENT),
+  ELEM(strong, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(style, PR_TRUE, PR_FALSE, GROUP_HEAD_CONTENT, GROUP_LEAF),
+  ELEM(sub, PR_TRUE, PR_TRUE, GROUP_SPECIAL, GROUP_INLINE_ELEMENT),
+  ELEM(sup, PR_TRUE, PR_TRUE, GROUP_SPECIAL, GROUP_INLINE_ELEMENT),
+  ELEM(table, PR_TRUE, PR_FALSE, GROUP_BLOCK, GROUP_TABLE_CONTENT),
+  ELEM(tbody, PR_TRUE, PR_FALSE, GROUP_TABLE_CONTENT, GROUP_TBODY_CONTENT),
+  ELEM(td, PR_TRUE, PR_FALSE, GROUP_TR_CONTENT, GROUP_FLOW_ELEMENT),
+  ELEM(textarea, PR_TRUE, PR_FALSE, GROUP_FORMCONTROL, GROUP_LEAF),
+  ELEM(tfoot, PR_TRUE, PR_FALSE, GROUP_NONE, GROUP_TBODY_CONTENT),
+  ELEM(th, PR_TRUE, PR_FALSE, GROUP_TR_CONTENT, GROUP_FLOW_ELEMENT),
+  ELEM(thead, PR_TRUE, PR_FALSE, GROUP_NONE, GROUP_TBODY_CONTENT),
+  ELEM(title, PR_TRUE, PR_FALSE, GROUP_HEAD_CONTENT, GROUP_LEAF),
+  ELEM(tr, PR_TRUE, PR_FALSE, GROUP_TBODY_CONTENT, GROUP_TR_CONTENT),
+  ELEM(tt, PR_TRUE, PR_TRUE, GROUP_FONTSTYLE, GROUP_INLINE_ELEMENT),
+  ELEM(u, PR_TRUE, PR_TRUE, GROUP_FONTSTYLE, GROUP_INLINE_ELEMENT),
+  // XXX Can contain self and ol because editor does sublists illegally.
+  ELEM(ul, PR_TRUE, PR_TRUE, GROUP_BLOCK | GROUP_OL_UL,
+       GROUP_LI | GROUP_OL_UL),
+  ELEM(var, PR_TRUE, PR_TRUE, GROUP_PHRASE, GROUP_INLINE_ELEMENT),
+  ELEM(wbr, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(xmp, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+
+  // These aren't elements.
+  ELEM(text, PR_FALSE, PR_FALSE, GROUP_LEAF, GROUP_NONE),
+  ELEM(whitespace, PR_FALSE, PR_FALSE, GROUP_LEAF, GROUP_NONE),
+  ELEM(newline, PR_FALSE, PR_FALSE, GROUP_LEAF, GROUP_NONE),
+  ELEM(comment, PR_FALSE, PR_FALSE, GROUP_LEAF, GROUP_NONE),
+  ELEM(entity, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(doctypeDecl, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(markupDecl, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+  ELEM(instruction, PR_FALSE, PR_FALSE, GROUP_NONE, GROUP_NONE),
+
+  ELEM(userdefined, PR_TRUE, PR_FALSE, GROUP_NONE, GROUP_FLOW_ELEMENT)
+};
+
+PRBool
+nsHTMLEditUtils::CanContain(PRInt32 aParent, PRInt32 aChild)
+{
+  NS_ASSERTION(aParent > eHTMLTag_unknown && aParent <= eHTMLTag_userdefined,
+               "aParent out of range!");
+  NS_ASSERTION(aChild > eHTMLTag_unknown && aChild <= eHTMLTag_userdefined,
+               "aChild out of range!");
+
+#ifdef DEBUG
+  static PRBool checked = PR_FALSE;
+  if (!checked) {
+    checked = PR_TRUE;
+    PRInt32 i;
+    for (i = 1; i <= eHTMLTag_userdefined; ++i) {
+      NS_ASSERTION(kElements[i - 1].mTag == i,
+                   "You need to update kElements (missing tags).");
+    }
+  }
+#endif
+
+  // Special-case button.
+  if (aParent == eHTMLTag_button) {
+    static const eHTMLTags kButtonExcludeKids[] = {
+      eHTMLTag_a,
+      eHTMLTag_fieldset,
+      eHTMLTag_form,
+      eHTMLTag_iframe,
+      eHTMLTag_input,
+      eHTMLTag_isindex,
+      eHTMLTag_select,
+      eHTMLTag_textarea
+    };
+
+    PRUint32 j;
+    for (j = 0; j < NS_ARRAY_LENGTH(kButtonExcludeKids); ++j) {
+      if (kButtonExcludeKids[j] == aChild) {
+        return PR_FALSE;
+      }
+    }
+  }
+
+  // Deprecated elements.
+  if (aChild == eHTMLTag_bgsound || aChild == eHTMLTag_keygen) {
+    return PR_FALSE;
+  }
+
+  // Bug #67007, dont strip userdefined tags.
+  if (aChild == eHTMLTag_userdefined) {
+    return PR_TRUE;
+  }
+
+  const nsElementInfo& parent = kElements[aParent - 1];
+  if (aParent == aChild) {
+    return parent.mCanContainSelf;
+  }
+
+  const nsElementInfo& child = kElements[aChild - 1];
+  return (parent.mCanContainGroups & child.mGroup) != 0;
+} 
+
+PRBool
+nsHTMLEditUtils::IsContainer(PRInt32 aTag)
+{
+  NS_ASSERTION(aTag > eHTMLTag_unknown && aTag <= eHTMLTag_userdefined,
+               "aTag out of range!");
+
+  return kElements[aTag - 1].mIsContainer;
+}
diff --git a/editor/libeditor/html/nsHTMLEditUtils.h b/editor/libeditor/html/nsHTMLEditUtils.h
index 9d3f8a72b70..eb57843d02d 100644
--- a/editor/libeditor/html/nsHTMLEditUtils.h
+++ b/editor/libeditor/html/nsHTMLEditUtils.h
@@ -79,7 +79,8 @@ public:
   static PRBool IsMailCite(nsIDOMNode *aNode);
   static PRBool IsFormWidget(nsIDOMNode *aNode);
   static PRBool SupportsAlignAttr(nsIDOMNode *aNode);
-
+  static PRBool CanContain(PRInt32 aParent, PRInt32 aChild);
+  static PRBool IsContainer(PRInt32 aTag);
 };
 
 #endif /* nsHTMLEditUtils_h__ */
diff --git a/editor/libeditor/html/nsHTMLEditor.cpp b/editor/libeditor/html/nsHTMLEditor.cpp
index e62c38bf56c..561a36f65b0 100644
--- a/editor/libeditor/html/nsHTMLEditor.cpp
+++ b/editor/libeditor/html/nsHTMLEditor.cpp
@@ -96,7 +96,6 @@
 #include "nsIDOMDocumentFragment.h"
 #include "nsIPresShell.h"
 #include "nsPresContext.h"
-#include "nsParserCIID.h"
 #include "nsIImage.h"
 #include "nsAOLCiter.h"
 #include "nsInternetCiter.h"
@@ -132,8 +131,6 @@
 #include "nsIWidget.h"
 #include "nsIParserService.h"
 
-static NS_DEFINE_CID(kCTransitionalDTDCID,  NS_CTRANSITIONAL_DTD_CID);
-
 // Some utilities to handle annoying overloading of "A" tag for link and named anchor
 static char hrefText[] = "href";
 static char anchorTxt[] = "anchor";
@@ -284,10 +281,6 @@ nsHTMLEditor::Init(nsIDOMDocument *aDoc, nsIPresShell *aPresShell,
     // block to scope nsAutoEditInitRulesTrigger
     nsAutoEditInitRulesTrigger rulesTrigger(NS_STATIC_CAST(nsPlaintextEditor*,this), rulesRes);
 
-    // Set up a DTD   
-    mDTD = do_CreateInstance(kCTransitionalDTDCID);
-    if (!mDTD) result = NS_ERROR_FAILURE;
-
     // Init the plaintext editor
     result = nsPlaintextEditor::Init(aDoc, aPresShell, aRoot, aSelCon, aFlags);
     if (NS_FAILED(result)) { return result; }
@@ -4266,40 +4259,37 @@ nsHTMLEditor::EndOperation()
 PRBool 
 nsHTMLEditor::TagCanContainTag(const nsAString& aParentTag, const nsAString& aChildTag)  
 {
-  // COtherDTD gives some unwanted results.  We override them here.
-  if (aParentTag.LowerCaseEqualsLiteral("ol") ||
-      aParentTag.LowerCaseEqualsLiteral("ul"))
-  {
-    // if parent is a list and tag is also a list, say "yes".
-    // This is because the editor does sublists illegally for now. 
-      if (aChildTag.LowerCaseEqualsLiteral("ol") ||
-          aChildTag.LowerCaseEqualsLiteral("ul"))
-      return PR_TRUE;
+  PRInt32 childTagEnum;
+  // XXX Should this handle #cdata-section too?
+  if (aChildTag.EqualsLiteral("#text")) {
+    childTagEnum = eHTMLTag_text;
+  }
+  else {
+    childTagEnum = sParserService->HTMLStringTagToId(aChildTag);
   }
 
-  if (aParentTag.LowerCaseEqualsLiteral("li"))
-  {
-    // list items cant contain list items
-    if (aChildTag.LowerCaseEqualsLiteral("li"))
-      return PR_FALSE;
+  PRInt32 parentTagEnum = sParserService->HTMLStringTagToId(aParentTag);
+  NS_ASSERTION(parentTagEnum < NS_HTML_TAG_MAX,
+               "Fix the caller, this type of node can never contain children.");
+
+  return nsHTMLEditUtils::CanContain(parentTagEnum, childTagEnum);
+}
+
+PRBool 
+nsHTMLEditor::IsContainer(nsIDOMNode *aNode)
+{
+  if (!aNode) {
+    return PR_FALSE;
   }
 
-/*  
-  // if parent is a pre, and child is not inline, say "no"
-  if ( aParentTag.EqualsLiteral("pre") )
-  {
-    if (aChildTag.EqualsLiteral("#text"))
-      return PR_TRUE;
+  nsAutoString stringTag;
 
-    PRInt32 childTagEnum = sParserService->HTMLStringTagToId(aChildTag);
-    PRInt32 parentTagEnum = sParserService->HTMLStringTagToId(aParentTag);
+  nsresult rv = aNode->GetNodeName(stringTag);
+  NS_ENSURE_SUCCESS(rv, PR_FALSE);
 
-    if (!mDTD->IsInlineElement(childTagEnum, parentTagEnum))
-      return PR_FALSE;
-  }
-*/
-  // else fall thru
-  return nsEditor::TagCanContainTag(aParentTag, aChildTag);
+  PRInt32 tagEnum = sParserService->HTMLStringTagToId(stringTag);
+
+  return nsHTMLEditUtils::IsContainer(tagEnum);
 }
 
 
diff --git a/editor/libeditor/html/nsHTMLEditor.h b/editor/libeditor/html/nsHTMLEditor.h
index 2eb2506c938..ada3efcf2ef 100644
--- a/editor/libeditor/html/nsHTMLEditor.h
+++ b/editor/libeditor/html/nsHTMLEditor.h
@@ -346,6 +346,9 @@ public:
   /** returns PR_TRUE if aParentTag can contain a child of type aChildTag */
   virtual PRBool TagCanContainTag(const nsAString& aParentTag, const nsAString& aChildTag);
   
+  /** returns PR_TRUE if aNode is a container */
+  virtual PRBool IsContainer(nsIDOMNode *aNode);
+
   /** make the given selection span the entire document */
   NS_IMETHOD SelectEntireDocument(nsISelection *aSelection);
 
diff --git a/parser/htmlparser/public/nsParserCIID.h b/parser/htmlparser/public/nsParserCIID.h
index a3758cc6f9d..70461e7f2bf 100644
--- a/parser/htmlparser/public/nsParserCIID.h
+++ b/parser/htmlparser/public/nsParserCIID.h
@@ -60,10 +60,6 @@
 #define NS_LOGGING_SINK_CID \
  {0xa6cf9060, 0x15b3, 0x11d2,{0x93, 0x2e, 0x00, 0x80, 0x5f, 0x8a, 0xdd, 0x32}}
 
-// {4611d482-960a-11d4-8eb0-b617661b6f7c}
-#define NS_CTRANSITIONAL_DTD_CID \
-{ 0x4611d482, 0x960a, 0x11d4, { 0x8e, 0xb0, 0xb6, 0x17, 0x66, 0x1b, 0x6f, 0x7c } }
-
 // {8323FAD0-2102-11d4-8142-000064657374}
 #define NS_VIEWSOURCE_DTD_CID \
 { 0x8323fad0, 0x2102, 0x11d4, { 0x81, 0x42, 0x0, 0x0, 0x64, 0x65, 0x73, 0x74 } }
diff --git a/parser/htmlparser/src/Makefile.in b/parser/htmlparser/src/Makefile.in
index af7c02ea10e..420790651ac 100644
--- a/parser/htmlparser/src/Makefile.in
+++ b/parser/htmlparser/src/Makefile.in
@@ -82,7 +82,6 @@ CPPSRCS = \
 		nsElementTable.cpp  \
 		nsExpatDriver.cpp   \
 		CNavDTD.cpp         \
-		COtherDTD.cpp       \
 		nsHTMLEntities.cpp  \
 		nsHTMLTags.cpp      \
 		nsHTMLTokens.cpp    \
diff --git a/parser/htmlparser/src/nsParser.cpp b/parser/htmlparser/src/nsParser.cpp
index a0133845d82..31aab84aa07 100644
--- a/parser/htmlparser/src/nsParser.cpp
+++ b/parser/htmlparser/src/nsParser.cpp
@@ -50,7 +50,6 @@
 #include "nsICharsetAlias.h"
 #include "nsIInputStream.h"
 #include "CNavDTD.h"
-#include "COtherDTD.h"
 #include "prenv.h" 
 #include "nsParserCIID.h"
 #include "nsReadableUtils.h"
diff --git a/parser/htmlparser/src/nsParserModule.cpp b/parser/htmlparser/src/nsParserModule.cpp
index 4be865ca3c9..a5f8226c35f 100644
--- a/parser/htmlparser/src/nsParserModule.cpp
+++ b/parser/htmlparser/src/nsParserModule.cpp
@@ -45,7 +45,6 @@
 #include "nsParserCIID.h"
 #include "nsParser.h"
 #include "CNavDTD.h"
-#include "COtherDTD.h"
 #include "nsHTMLEntities.h"
 #include "nsHTMLTokenizer.h"
 //#include "nsTextTokenizer.h"
@@ -70,7 +69,6 @@ NS_GENERIC_FACTORY_CONSTRUCTOR(nsExpatDriver)
 
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsParser)
 NS_GENERIC_FACTORY_CONSTRUCTOR(CNavDTD)
-NS_GENERIC_FACTORY_CONSTRUCTOR(CTransitionalDTD)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsParserService)
 
 #ifdef MOZ_VIEW_SOURCE
@@ -86,8 +84,6 @@ static const nsModuleComponentInfo gComponents[] = {
 
   { "Parser", NS_PARSER_CID, NULL, nsParserConstructor },
   { "Navigator HTML DTD", NS_CNAVDTD_CID, NULL, CNavDTDConstructor },
-  { "Transitional DTD", NS_CTRANSITIONAL_DTD_CID, NULL,
-    CTransitionalDTDConstructor },
 #ifdef MOZ_VIEW_SOURCE
   { "ViewSource DTD", NS_VIEWSOURCE_DTD_CID, NULL, CViewSourceHTMLConstructor },
 #endif
diff --git a/parser/htmlparser/src/nsViewSourceHTML.cpp b/parser/htmlparser/src/nsViewSourceHTML.cpp
index 32cd11488bd..50876e2089d 100644
--- a/parser/htmlparser/src/nsViewSourceHTML.cpp
+++ b/parser/htmlparser/src/nsViewSourceHTML.cpp
@@ -84,7 +84,6 @@
 
 #include "nsIServiceManager.h"
 
-#include "COtherDTD.h"
 #include "nsElementTable.h"
 
 #include "prenv.h"  //this is here for debug reasons...