Putting an SVG element in the editor content will throw an exception under IE.
Workaround (Make sure to add the script element with the fix right after the RadEditor declaration):
<telerik:RadEditor runat="server" ID="RadEditor1">
<Content>
<svg height="100" width="100">
<circle cx="50" cy="50" r="40" stroke="black" stroke-width="3" fill="red" />
</svg>
</Content>
</telerik:RadEditor>
<script type="text/javascript">
var oldMarkListItems = Telerik.Web.UI.Editor.WordListConverter.prototype.markListItems;
Telerik.Web.UI.Editor.WordListConverter.prototype.markListItems = function(htmlText)
{
if (!htmlText)
return htmlText;
return oldMarkListItems.call(this, htmlText);
};
</script>