Let's say I have that basic html list :

    <ul id="target">
        <li>item a</li>
        <li>item b
            <ul id="source">
                <li>sub item a</li>
                <li>sub item b</li>
                <li>sub item c</li>
            </ul>
        </li>
        <li>item c</li>
    </ul>

I want to point to the element <ul id="target"> using the element <ul id="source">.

I do :

 $("#source").closest("ul"); // return the element <ul id="source">

It point on itself where it should return the element <UL id="target">

If I use :

$("#source").closest("ul#target"); // return <ul id="target">

It works as expected.