Creating Self closing Tags using SimpleXMLElement

I have to create an xml string to be sent in a post request. I am using SimpleXMLElement library of PHP to create xml for the same.

I want to create a nested xml with one of the tag as self closing.

So Far I have created tags with elements having attributes and children as follows

$envelop = new SimpleXMLElement("<Envelope></Envelope>");
$body = $envelop->addChild('Body');
.
.
.
.
$envelop->asXML(); // Gives me proper XML

What I want to achieve using SimpleXMLElement element now is a self closing tag.

<Envelope>
 <Body>
  <ExportList>
   <LIST_ID>234234</LIST_ID>
   <EXPORT_TYPE>ALL</EXPORT_TYPE>
   <EXPORT_FORMAT>CSV</EXPORT_FORMAT>
   <ADD_TO_STORED_FILES/>                 < -- Target Tag -->
   <DATE_START>07/25/2003 12:12:11</DATE_START>
   <DATE_END>09/30/2005 14:14:11</DATE_END>
   </ExportList>
 </Body>
</Envelope>

I tried searching for solutions and docs. But I was not able to find any any solutions for this one. Please if anybody could help in achieving the above task.

Also FYI I've got solutions using DOMElement, but I am not interested in using that, cause then I will need to re write my whole application. Please let me know if this can be achieved using SimpleXMLElement.

Solution

While I was running by head around so impatiently for the solution, in the end it was really simple. It was mentioned no where, I just tried adding a tag with no second parameter to a parent tag. Simple(XMLElemet) as that :P

Below is the code:

$envelop = new SimpleXMLElement("<Envelope></Envelope>");
$body = $envelop->addChild('Body');
$exportList = $body->addChild('ExportList');
$exportList->addChild('LIST_ID', 234234);
$exportList->addChild('ADD_TO_STORED_FILES'); // passing nothing
.
.
.
$envelop->asXML();

Conclusion : So basically if its a leaf node with no data, it will be created as self closing.

Now I need to check how to create a leaf node with non self closing tag. That will be another question. But later :)

For now I am Done!