           <div id="middle_child"></div>
                            <div id="youngest_child"></div>
                        </span>
                    </div>
                    <span class="a" id="between_siblings1" data-locator="between_siblings1"></span>
                    <div class="b" id="second_sibling" data-locator="second_sibling">Second</div>
                    <span class="a" id="between_siblings2" data-locator="between_siblings2"></span>
                    <div class="a b" id="third_sibling