Jquery Get last row of table within last element in a series
<div id="slides">
    <section id="first">
        <section>
            <table>
                <thead>
                </thead>
                <tbody>
                    <tr id="somethingUnique">
                    ...
                    </tr>
                </tbody>
            </table>
        </section>
        <section>
            <table>
                <thead>
                </thead>
                <tbody>
                    <tr id="somethingUnique">
                    ...
                    </tr>
                </tbody>
            </table>
        </section>
       ...
    </section>
</div>

var lastListItem = $('#first:last-child table>tbody>tr:last').attr("id");
    alert(lastListItem);

$('#first table:last tr:last')

$('#first tr:last')

var lastListItem = $('#first section:last  table tr:last').attr("id");

var lastListItem = $("#first").find("section").last().find("tr").last().attr("id");

​$("#first")​.find("tr:last").attr("id")

$("#first tr:last").attr("id")

$('#first section:last-child table>tbody>tr:last').attr("id");

$('#first section:last-child tr:last-child').attr("id");