Update: 2014 March 19 - domReady version II has been created that provides a streamlined domReady function.
Update: 2007 Oct 25 - DOMContentLoaded Event for Browsers, Part IV has been created that adds a fix for calling DOMContentLoaded after the DOMContentLoaded event has occurred. Please check it out.
The DOMContentLoaded event allows you to add behavior or change the HTML of a page after the HTML has loaded and before the onload event which happens after the complete page, including images has loaded. This allows you to add menu, tree behavior, AJAX functionality or anything else without having to wait for all items on a page to load. You may have experienced the need for a DOMContentLoaded event on a page that includes drop down menus or a tabbed interface which doesn't work until all images have loaded. Using the DOMContentLoaded event allows you to add the behavior before images and objects have loaded.