Here's a simple, recursive, function to transform XML data into pseudo E4X syntax ie. root.child.value = foobar

<?php
error_reporting(E_ALL);

$xml = new SimpleXMLElement(
'<Patriarch>
   <name>Bill</name>
   <wife>
     <name>Vi</name>
   </wife>
   <son>
     <name>Bill</name>
   </son>
   <daughter>
     <name>Jeri</name>
     <husband>
       <name>Mark</name>
     </husband>
     <son>
       <name>Greg</name>
     </son>
     <son>
       <name>Tim</name>
     </son>     
     <son>
       <name>Mark</name>
     </son>     
     <son>
       <name>Josh</name>
         <wife>
           <name>Kristine</name>
         </wife> 
         <son>
           <name>Blake</name>
         </son>
         <daughter>
           <name>Liah</name>
         </daughter>
     </son>
   </daughter>
</Patriarch>');

RecurseXML($xml);

function RecurseXML($xml,$parent="")
{
   $child_count = 0;
   foreach($xml as $key=>$value)
   {
      $child_count++;     
      if(RecurseXML($value,$parent.".".$key) == 0)  // no childern, aka "leaf node"
      {
         print($parent . "." . (string)$key . " = " . (string)$value . "<BR>\n");        
      }     
   }
   return $child_count;
}

?>

The output....

.name = Bill
.wife.name = Vi
.son.name = Bill
.daughter.name = Jeri
.daughter.husband.name = Mark
.daughter.son.name = Greg
.daughter.son.name = Tim
.daughter.son.name = Mark
.daughter.son.name = Josh
.daughter.son.wife.name = Kristine
.daughter.son.son.name = Blake
.daughter.son.daughter.name = Liah

Just a quick addition:

If you need to access a child node which contains a dash, you need to encapsulate it with {""}.

For example:
<?php
foreach ($domain->domain-listing as $product) {
}
?>

The example above doesn't work because of the dash. But instead you need to use:
<?php
foreach ($domain->{"domain-listing"} as $product) {
}
?>

At least for me the second example works perfectly fine.

I made a slightly differnt approch towards the RecurseXML function. Beeing hungry I had problems with the code, as it did just overwrite two <maincourse>s. So here is what I did:

<?php

$xml = new SimpleXMLElement(
'<meal>
   <type>Lunch</type>
   <time>12:30</time>
   <menu>
     <entree>salad</entree>
     <maincourse>
        <part>ships</part>
        <part>steak</part>
     </maincourse>
     <maincourse>
        <part>fisch</part>
        <part>rice</part>
     </maincourse>
     <maincourse>
        <part>wine</part>
        <part>cheese</part>
     </maincourse>
   </menu>
</meal>');

$vals = array();
RecurseXML($xml,$vals);

foreach($vals as $key=>$value)
  print("{$key} = {$value}<BR>\n");

function RecurseXML($xml,&$vals,$parent="") {

  $childs=0;
  $child_count=-1; # Not realy needed.
  $arr=array();
        foreach ($xml->children() as $key=>$value) {
                if (in_array($key,$arr)) {
                        $child_count++;
                } else {
                        $child_count=0;
                }
                $arr[]=$key;
                $k=($parent == "") ? "$key.$child_count" : "$parent.$key.$child_count";
                $childs=RecurseXML($value,$vals,$k);
                if ($childs==0) {
                        $vals[$k]= (string)$value;
                }
        }

  return $childs;
}

?>
Output is like this:
type.0 = Lunch
time.0 = 12:30
menu.0.entree.0 = salad
menu.0.maincourse.0.part.0 = ships
menu.0.maincourse.0.part.1 = steak
menu.0.maincourse.0 =
menu.0.maincourse.1.part.0 = fisch
menu.0.maincourse.1.part.1 = rice
menu.0.maincourse.1 =
menu.0.maincourse.2.part.0 = wine
menu.0.maincourse.2.part.1 = cheese
menu.0.maincourse.2 =
menu.0 = 

(Not beautiful, but it solved my case...)

SimpleXMLElement::children can return null in this case:

<?php 
$xml = '
<root attr="Hello"/>
';

$sxe = new SimpleXMLElement($xml);

$sxe_xpath = $sxe->xpath('/root/@attr')[0];

$children = $sxe_xpath->children();

var_export($children); // Is null
?>