add prettyprint class dynamically - to be used in conjunction with https://code.google.com/p/google-code-prettify/

prettifyRun.js

;(function() {
  var pres = document.getElementsByTagName("pre");

  for(var i=0; i < pres.length; i++) {
    if(pres[i].getElementsByTagName('code').length > 0)
    {
      pres[i].className += "prettyprint";
    }
  }

  prettyPrint();
})();