(PHP 5, PHP 7, PHP 8)
DOMElement::setAttribute — Adds new or modifies existing attribute
   Sets an attribute with name qualifiedName to the given
   value. If the attribute does not exist, it will be created.
  
qualifiedNameThe name of the attribute.
valueThe value of the attribute.
Example #1 Setting an attribute
<?php
$doc = new DOMDocument("1.0");
$node = $doc->createElement("para");
$newnode = $doc->appendChild($node);
$newnode->setAttribute("align", "left");
?>