a.php

#!/usr/bin/php
<?php
class HtmlTable extends DOMElement
{   
        public function __construct($height, $width)
        {   
                parent::__construct("table");
                for ($i = 0; $i < $height; ++$i) {
                        $row = $this->appendChild(new DOMElement("tr"));
                        for($j = 0; $j < $width; ++$j) {
                                $row->appendChild(new DOMElement("td"));
                        }   
                }   
        }   
}   

$document = new DOMDocument("1.0", "UTF-8");
$document->registerNodeClass("DOMElement", "HtmlTable");
$document->appendChild(new HtmlTable(3, 2));
$document->saveXML();

Running it gets

Fatal error: Uncaught exception 'DOMException' with message 'No Modification Allowed Error' in /home/www/a.php:9
Stack trace:
#0 /home/www/a.php(9): DOMNode->appendChild(Object(DOMElement))
#1 /home/www/a.php(19): HtmlTable->__construct(3, 2)
#2 {main}
  thrown in /home/www/a.php on line 9