Returns the content to display.
public function getContent() {
// Since this is a mock object, we just return some HTML of the desired
// nesting level. For depth=2, this returns:
// '<ul><li>1<ul><li>1.1</li></ul></li></ul>'.
$content = '';
for ($i = 0; $i < $this->depth; $i++) {
$content .= '<ul><li>' . implode('.', array_fill(0, $i + 1, '1'));
}
for ($i = 0; $i < $this->depth; $i++) {
$content .= '</li></ul>';
}
return $content;
}