SVG: scoped is passed as metadata

Instead of using a svg class to pass scope information
use notebook metadata.

Suggested by Matthias Bussonnier

IPython/core/display.py

@@ -395,8 +395,6 b' class SVG(DisplayObject):'
     def data(self):
         return self._data
 
-    _scoped_class = "ipython-scoped"
-
     @data.setter
     def data(self, svg):
         if svg is None:
@@ -409,12 +407,6 b' class SVG(DisplayObject):'
         # get svg tag (should be 1)
         found_svg = x.getElementsByTagName('svg')
         if found_svg:
-            # If the user requests scoping, tag the svg with the
-            # ipython-scoped class
-            if self.scoped:
-                classes = (found_svg[0].getAttribute('class') +
-                           " " + self._scoped_class)
-                found_svg[0].setAttribute('class', classes)
             svg = found_svg[0].toxml()
         else:
             # fallback on the input, trust the user
@@ -424,7 +416,11 b' class SVG(DisplayObject):'
         self._data = svg
 
     def _repr_svg_(self):
-        return self.data
+        if self.scoped:
+            metadata = dict(scoped=True)
+            return self.data, metadata
+        else:
+            return self.data
 
 
 class JSON(DisplayObject):

IPython/html/static/notebook/js/outputarea.js

@@ -498,7 +498,7 b' var IPython = (function (IPython) {'
         wrapper.append(svg);
         var svg_element = wrapper.children()[0];
 
-        if (svg_element.classList.contains('ipython-scoped')) {
+        if (md['scoped']) {
             // To avoid style or use collisions between multiple svg figures,
             // svg figures are wrapped inside an iframe.
             var iframe = $('<iframe/>')