diff --git a/unpacked/MathJax.js b/unpacked/MathJax.js
index 1af0c0a08..75a6ad88f 100644
--- a/unpacked/MathJax.js
+++ b/unpacked/MathJax.js
@@ -1852,7 +1852,8 @@ MathJax.Hub = {
       locale: "en",        //  the language to use for messages
       mpContext: false,    //  true means pass menu events to MathPlayer in IE
       mpMouse: false,      //  true means pass mouse events to MathPlayer in IE
-      texHints: true       //  include class names for TeXAtom elements
+      texHints: true,      //  include class names for TeXAtom elements
+      semantics: false     //  add semantics tag with original form in MathML output
     },
     
     errorSettings: {
diff --git a/unpacked/config/default.js b/unpacked/config/default.js
index 995383980..38cca24a8 100644
--- a/unpacked/config/default.js
+++ b/unpacked/config/default.js
@@ -243,7 +243,8 @@ MathJax.Hub.Config({
     context: "MathJax",  //  or "Browser" for pass-through to browser menu
     mpContext: false,    //  true means pass menu events to MathPlayer in IE
     mpMouse: false,      //  true means pass mouse events to MathPlayer in IE
-    texHints: true       //  include class names for TeXAtom elements
+    texHints: true,      //  include class names for TeXAtom elements
+    semantics: false     //  add semantics tag with original form in MathML output
   },
   
   //
diff --git a/unpacked/extensions/MathEvents.js b/unpacked/extensions/MathEvents.js
index 381548e78..16ee6e603 100644
--- a/unpacked/extensions/MathEvents.js
+++ b/unpacked/extensions/MathEvents.js
@@ -160,6 +160,7 @@
 	  source.items[0].name = jax.sourceMenuTitle;
 	  source.items[0].format = (jax.sourceMenuFormat||"MathML");
           source.items[1].name = INPUT[jax.inputJax].sourceMenuTitle;
+          source.items[5].disabled = !INPUT[jax.inputJax].annotationEncoding;
 
           // 
           // Try and find each known annotation format and enable the menu
diff --git a/unpacked/extensions/MathMenu.js b/unpacked/extensions/MathMenu.js
index b60e2afb0..0d60a8d8f 100644
--- a/unpacked/extensions/MathMenu.js
+++ b/unpacked/extensions/MathMenu.js
@@ -717,7 +717,7 @@
       var MML = MathJax.ElementJax.mml;
       if (MML && typeof(MML.mbase.prototype.toMathML) !== "undefined") {
         // toMathML() can call MathJax.Hub.RestartAfter, so trap errors and check
-        try {MENU.ShowSource.Text(MENU.jax.root.toMathML(),event)} catch (err) {
+        try {MENU.ShowSource.Text(MENU.jax.root.toMathML("",MENU.jax),event)} catch (err) {
           if (!err.restart) {throw err}
           CALLBACK.After([this,MENU.ShowSource,EVENT],err.restart);
         }
@@ -1060,7 +1060,8 @@
         ITEM.COMMAND(["Original","Original Form"],  MENU.ShowSource, {nativeTouch: true}),
         ITEM.SUBMENU(["Annotation","Annotation"], {disabled:true}),
         ITEM.RULE(),
-        ITEM.CHECKBOX(["texHints","Show TeX hints in MathML"], "texHints")
+        ITEM.CHECKBOX(["texHints","Show TeX hints in MathML"], "texHints"),
+        ITEM.CHECKBOX(["semantics","Add original form as annotation"], "semantics")
       ),
       ITEM.RULE(),
       ITEM.SUBMENU(["Settings","Math Settings"],
diff --git a/unpacked/extensions/toMathML.js b/unpacked/extensions/toMathML.js
index a773201e2..4d1a4efa8 100644
--- a/unpacked/extensions/toMathML.js
+++ b/unpacked/extensions/toMathML.js
@@ -136,6 +136,38 @@ MathJax.Hub.Register.LoadHook("[MathJax]/jax/element/mml/jax.js",function () {
     }
   });
   
+  //
+  //  Override math.toMathML in order to add semantics tag
+  //  for the input format, if the user requests that in the
+  //  Show As menu.
+  //
+  MML.math.Augment({
+    toMathML: function (space,jax) {
+      var annotation;
+      if (space == null) {space = ""}
+      if (jax && jax.originalText && SETTINGS.semantics)
+        {annotation = MathJax.InputJax[jax.inputJax].annotationEncoding}
+      var nested = (this.data[0] && this.data[0].data.length > 1);
+      var tag = this.type, attr = this.toMathMLattributes();
+      var data = [], SPACE = space + (annotation ? "    " : "") + (nested ? "  " : "");
+      for (var i = 0, m = this.data.length; i < m; i++) {
+        if (this.data[i]) {data.push(this.data[i].toMathML(SPACE))}
+          else {data.push(SPACE+"<mrow />")}
+      }
+      if (data.length === 0 || (data.length === 1 && data[0] === "")) {
+        if (!annotation) {return "<"+tag+attr+" />"}
+        data.push(SPACE+"<mrow />");
+      }
+      if (annotation) {
+        if (nested) {data.unshift(space+"    <mrow>"); data.push(space+"    </mrow>")}
+        data.unshift(space+"  <semantics>");
+        data.push(space+'    <annotation encoding="'+annotation+'">'+jax.originalText+"</annotation>");
+        data.push(space+"  </semantics>");
+      }
+      return space+"<"+tag+attr+">\n"+data.join("\n")+"\n"+space+"</"+tag+">";
+    }
+  });
+  
   MML.msubsup.Augment({
     toMathML: function (space) {
       var tag = this.type;