While doing a select or any operations into XMLDB, you'll have 3 possible values in return:
Array
A node can be figured as an array in this format:
Array => ('name' => 'item'),
('attributes' => array('id'=>'1',
'name'=>'test')),
('childs' => array('visibility'=>'true',
'x'=>'32'))
This array is equal to
<item id="1" name="test">
<visibility>true</visibility>
<x>32</x>
</item>
Node
It's actually a "DOMNode": http://www.php.net/manual/fr/class.domnode.php
It's mainly use for Data manipulation
We usually use Array for display or manual operation
Count
Not really of format, but operation with this $format will return an Integer.