gistfile1.js

// invokes +callback+ on elements found by +selector+ that have an href property value
// equal to the current page (pathname). It is recommended to use a selector that selects
// anchor (a) elements.
function currentPage(selector, callback) {
  $$(selector).each(function(e) {
    if (e.href == document.URL) {
      callback.call(null, e);
    }
  })
}

// mark current nav item as selected. This is redundant for the navigation implemented
// in the app, but not for a snippet.
Event.onReady(function() {
  currentPage('#storyNavColumn ol a', function(e) { 
    e.addClassName('leftNavSelected');
  });
});