title: Using <switch> with <foreignObject> in SVG
body: <p>I am trying to properly implement the switch tag for a foreignObject tag in SVG so that Internet Explorer can display something else (nothing new in IE, always leaving features out). The documentation is <em>almost</em> perfectly clear on how to do this:</p>
  
  <pre class="lang-svg prettyprint-override"><code>&lt;switch&gt;
  &lt;!-- Process the embedded XHTML if the requiredExtensions attribute
       evaluates to true (i.e., the user agent supports XHTML
       embedded within SVG). --&gt;
  &lt;foreignObject width="100" height="50"
                 requiredExtensions="http://example.com/SVGExtensions/EmbeddedXHTML"&gt;
    &lt;!-- XHTML content goes here --&gt;
    &lt;body xmlns="http://www.w3.org/1999/xhtml"&gt;
      &lt;p&gt;Here is a paragraph that requires word wrap&lt;/p&gt;
    &lt;/body&gt;
  &lt;/foreignObject&gt;
  &lt;!-- Else, process the following alternate SVG.
       Note that there are no testing attributes on the 'text' element.
       If no testing attributes are provided, it is as if there
       were testing attributes and they evaluated to true.--&gt;
  &lt;text font-size="10" font-family="Verdana"&gt;
    &lt;tspan x="10" y="10"&gt;Here is a paragraph that&lt;/tspan&gt;
    &lt;tspan x="10" y="20"&gt;requires word wrap.&lt;/tspan&gt;
  &lt;/text&gt;
  </code></pre>
  
  <p></p>
  
  <p>The example is nice and clear and shows how to use the requiredExtensions attribute. However, the hyperlink "http://example.com/SVGExtensions/EmbeddedXHTML" is meaningless to me. What would I have to put in place of this in order to denote that XHTML is the requiredExtension for this foreignObject? </p>