If writing sub-elements and attributes is intermixed, any attempt to write
attributes after the first sub-element will fail and return false.
<?php
$xml = new XMLWriter();
$xml->openMemory();
$xml->startElement('element');
$xml->writeAttribute('attr1', '0');
$xml->writeElement('subelem', '0');
var_dump($xml->writeAttribute('attr2', '0'));
$xml->endElement();
echo $xml->flush();
?>
The above example will output:
bool(false)
<element attr1="0"><subelem>0</subelem></element>