[jQuery] continuously search for elements in a document

[rich]

(Using jQuery w/ ASP.NET 2.0)

I have a few error prompts that are in hidden spans inside <li>'s.  I
need to hide the LI's when the error prompt is hidden.

Example:
$(document).ready(function() {
    //hide empty error spans
    $('ul.errors li span').each(function(i){
        if($(this).css("display") == "none") {
            $(this).parent().hide();
        };
    });
});

This works, but only on page load.  These error prompts display as
needed on onBlur (via .NET default methods).

How can I continuously scan the document for these error prompts and
show/hide the parent LI's when the prompts show/hide?

Thanks,
-rich