diff -r 000000000000 -r 6474c204b198 layout/mathml/nsMathMLsemanticsFrame.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/mathml/nsMathMLsemanticsFrame.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,120 @@
+/* -*- 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 "nsMathMLsemanticsFrame.h"
+#include "nsMimeTypes.h"
+#include "mozilla/gfx/2D.h"
+
+//
+// <semantics> -- associate annotations with a MathML expression
+//
+
+nsIFrame*
+NS_NewMathMLsemanticsFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
+{
+  return new (aPresShell) nsMathMLsemanticsFrame(aContext);
+}
+
+NS_IMPL_FRAMEARENA_HELPERS(nsMathMLsemanticsFrame)
+
+nsMathMLsemanticsFrame::~nsMathMLsemanticsFrame()
+{
+}
+
+nsIFrame* 
+nsMathMLsemanticsFrame::GetSelectedFrame()
+{
+  // By default, we will display the first child of the <semantics> element.
+  nsIFrame* childFrame = mFrames.FirstChild(); 
+  mSelectedFrame = childFrame;
+
+  // An empty <semantics> is invalid
+  if (!childFrame) {
+    mInvalidMarkup = true;
+    return mSelectedFrame;
+  }
+  mInvalidMarkup = false;
+
+  // Using <annotation> or <annotation-xml> as a first child is invalid.
+  // However some people use this syntax so we take care of this case too.
+  bool firstChildIsAnnotation = false;
+  nsIContent* childContent = childFrame->GetContent();
+  if (childContent->GetNameSpaceID() == kNameSpaceID_MathML &&
+      (childContent->Tag() == nsGkAtoms::annotation_ ||
+       childContent->Tag() == nsGkAtoms::annotation_xml_)) {
+    firstChildIsAnnotation = true;
+  }
+
+  // If the first child is a presentation MathML element other than
+  // <annotation> or <annotation-xml>, we are done.
+  if (!firstChildIsAnnotation &&
+      childFrame->IsFrameOfType(nsIFrame::eMathML)) {
+    nsIMathMLFrame* mathMLFrame = do_QueryFrame(childFrame);
+    if (mathMLFrame) {
+      TransmitAutomaticData();
+      return mSelectedFrame;
+    }
+    // The first child is not an annotation, so skip it.
+    childFrame = childFrame->GetNextSibling();
+  }
+
+  // Otherwise, we read the list of annotations and select the first one that
+  // could be displayed in place of the first child of <semantics>. If none is
+  // found, we fallback to this first child.
+  for ( ; childFrame; childFrame = childFrame->GetNextSibling()) {
+    nsIContent* childContent = childFrame->GetContent();
+
+    if (childContent->GetNameSpaceID() != kNameSpaceID_MathML) continue;
+
+    if (childContent->Tag() == nsGkAtoms::annotation_) {
+
+      // If the <annotation> element has an src attribute we ignore it.
+      // XXXfredw Should annotation images be supported? See the related
+      // bug 297465 for mglyph.
+      if (childContent->HasAttr(kNameSpaceID_None, nsGkAtoms::src)) continue;
+
+      // Otherwise, we assume it is a text annotation that can always be
+      // displayed and stop here.
+      mSelectedFrame = childFrame;
+      break;
+    }
+
+    if (childContent->Tag() == nsGkAtoms::annotation_xml_) {
+
+      // If the <annotation-xml> element has an src attribute we ignore it.
+      if (childContent->HasAttr(kNameSpaceID_None, nsGkAtoms::src)) continue;
+
+      // If the <annotation-xml> element has an encoding attribute
+      // describing presentation MathML, SVG or HTML we assume the content
+      // can be displayed and stop here.
+      //
+      // We recognize the following encoding values:
+      //
+      // - "MathML-Presentation", which is mentioned in the MathML3 REC
+      // - "SVG1.1" which is mentioned in the W3C note
+      //                   http://www.w3.org/Math/Documents/Notes/graphics.xml
+      // - Other mime Content-Types for SVG and HTML
+      //
+      // We exclude APPLICATION_MATHML_XML = "application/mathml+xml" which
+      // is ambiguous about whether it is Presentation or Content MathML.
+      // Authors must use a more explicit encoding value.
+      nsAutoString value;
+      childContent->GetAttr(kNameSpaceID_None, nsGkAtoms::encoding, value);
+      if (value.EqualsLiteral("application/mathml-presentation+xml") ||
+          value.EqualsLiteral("MathML-Presentation") ||
+          value.EqualsLiteral(IMAGE_SVG_XML) ||
+          value.EqualsLiteral("SVG1.1") ||
+          value.EqualsLiteral(APPLICATION_XHTML_XML) ||
+          value.EqualsLiteral(TEXT_HTML)) {
+        mSelectedFrame = childFrame;
+        break;
+      }
+    }
+  }
+
+  TransmitAutomaticData();
+  return mSelectedFrame;
+}