...
   Element Node
           [
             $parent, # node_parent
             <position in current array>, # node_pos
             'xxx', # node_prefix - namespace prefix on this element
             [ ... ], # node_children
             'yyy', # node_name - element tag name
             [ ... ], # node_attribs - attributes on this element
             [ ... ], # node_namespaces - namespaces currently in scope
           ]

   Attribute Node
           [
             $parent, # node_parent - the element node
             <position in current array>, # node_pos
             'xxx', # node_prefix - namespace prefix on this element
             'href', # node_key - attribute name
             'ftp://ftp.com/', # node_value - value in the node
           ]
...