(PHP 5)
DOMElement::setAttribute — Adds new attribute
   Sets an attribute with name name to the given
   value. If the attribute does not exist, it will be created.
  
name
     The name of the attribute.
value
     The value of the attribute.
   The new DOMAttr or FALSE if an error occurred.
  
DOM_NO_MODIFICATION_ALLOWED_ERR
     Raised if the node is readonly.
Example #1 Setting an attribute
<?php
$doc = new DOMDocument("1.0");
$node = $doc->createElement("para");
$newnode = $doc->appendChild($node);
$newnode->setAttribute("align", "left");
?>