var XHTML = "http://www.w3.org/1999/xhtml";

function stripPrefix(id)
{
  return id.replace(/^update_/, "");
}

function updateClasses(currentDatetime)
{
  var inses = document.getElementsByTagNameNS(XHTML, "ins");

  for(var i = 0; i < inses.length; i++)
  {
    var ins = inses[i];

    var datetime = ins.getAttribute("datetime");

    if(datetime == currentDatetime)
    {
      ins.className = 'current';
    }
    else
    {
      ins.className = null;
    }
  }
}

function updateClassesFromURL(e)
{
  var url = document.location.href;

  if(!url.match(/#/))
  {
    return;
  }

  var anchorName = url.replace(/.*#/, "");
  var datetime = stripPrefix(anchorName);

  updateClasses(datetime);
}

window.addEventListener('load', updateClassesFromURL, false);