First and last elements in list using RecursiveIteratorIterator

I'm using RecursiveIteratorIterator to loop over Zend_Navigation, which is basically a list of nested <ul> and <li> tags:

$iterator = new RecursiveIteratorIterator(
    $co开发者_如何学Cntainer, 
    RecursiveIteratorIterator::CHILD_FIRST
);
foreach ($iterator as $page) {
    ...
    // isLast()?
    // isFirst()?
}

How to determine, whether the currently iterated element ($page) is first or last element on current level?

I need to add first and last class attribute to those elements.

---

You could use getDepth() to query the depth of the tag. When the depth increases, you're at a new level and should add a first attribute. When the depth decreases between tags, that tells you the previous tag was the last in its level and you should add a last attribute to it. This means you will have to read the next tag before you can finish processing the current tag.