> Why does replaceAll only seem to work once in this example? I guess you meant replaceWith?
> $("#hello").replaceWith("foo");
Once this code executes, it has replaced the element with
id="hello" (and any children) with the string "foo". There is no
longer a #hello in the document.
http://docs.jquery.com/Manipulation/replaceWith#content
If you just want to replace the stuff inside #hello, try $
("#hello").empty().append("foo") or $("hello").html("foo").
