XPath iteration problem

[squariegoes]

Hi I want to be able to iterate over the children of the book element but don't know how to do it.  The childrens names will change between queries so the child must work dynamically.  Is there any way of cycling through the chlidren of an element using []? Here's what I've got so far -

 

if($xml->book[0]->child[1]->attributes() == true){
echo 'attribute found';
}