Google Sites gadget to include a tweet button

Tweet_Button.xml

<?xml version="1.0" encoding="UTF-8" ?>
<Module>
  <ModulePrefs title="Tweet Button" title_url="http://www.opensourceteacher.ca/apps-script/tweet-button"
          description="Add a button to let your website viewers tweet right from your pages."
          thumbnail="http://www.gstatic.com/sites-gadgets/common/images/sites-icon-gadget-thumb.png"
          screenshot="http://www.gstatic.com/sites-gadgets/common/images/sites-icon-gadget-ss.png"
          height="23" width="65" author="Open Source Teacher">
  </ModulePrefs>
    <UserPref name="handle" display_name="Twitter Handle (no @ symbol)" required="true"/>
    <UserPref name="message" display_name="Tweet content text" required="true"/>
    <UserPref name="hashtag" display_name="Hashtag (optional)" required="false"/>
  <Content type="html">
      <![CDATA[
<style>
body, img a,a img {
  background-color: transparent;
}
</style>
    <a id="tweetButton" href="https://twitter.com/share" class="twitter-share-button" data-text="This tweet button courtesy of Open Source Teacher" data-url="http://www.opensourceteacher.ca" data-via="jpetersen02" data-hashtags="">Tweet</a>
  <script type="text/javascript">
  gadgets.util.registerOnLoadHandler(doRender);
    function doRender() {
      !function(d,s,id){
        var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';
        if(!d.getElementById(id)){
            js=d.createElement(s);
            js.id=id;
            js.src=p+"://platform.twitter.com/widgets.js";
            fjs.parentNode.insertBefore(js,fjs);
        }
      var canonical = document.referrer;
        document.getElementById("tweetButton").setAttribute("data-url",canonical);
        var prefs = new gadgets.Prefs();
        var text = prefs.getString("message");
        var handle = prefs.getString("handle");
        var hashtag = prefs.getString("hashtag");
        if (hashtag[0] == "#") {
            hashtag = hashtag.substr(1,hashtag.length);
        }
        document.getElementById("tweetButton").setAttribute("data-text",text);    
        document.getElementById("tweetButton").setAttribute("data-via",handle);
        document.getElementById("tweetButton").setAttribute("data-hashtags",hashtag);
      }
      (document, 'script', 'twitter-wjs');
      }
  </script>
]]>
  </Content>
</Module>