http://lhorie.blogspot.com/2007/03/getelementsbyclassname-speed.html

http://ejohn.org/blog/getelementsbyclassname-speed-comparison/

while(item = iterator.iterateNext())
{
// do something with item
} 

http://developer.mozilla.org/en/docs/DOM:document.getElementsByClassName

http://developer.mozilla.org/en/docs/Introduction_to_using_XPath_in_JavaScript
http://developer.mozilla.org/en/docs/DOM:document.evaluate

attachEvent 

http://www.google.com/search?num=100&q=attachEvent%20addEventListener