Self-closing tags using createElement

I need to add a self-closing tag to XML file with DOM in PHP, but I don't know how, because standardly, this tag looks like this:

<tag></tag>

But it should look like this:

<tag/>

DOM will do that automatically for you

$dom = new DOMDocument;
$dom->appendChild($dom->createElement('foo'));
echo $dom->saveXml();

will give by default

<?xml version="1.0"?>
<foo/>

unless you do

$dom = new DOMDocument;
$dom->appendChild($dom->createElement('foo'));
echo $dom->saveXml($dom, LIBXML_NOEMPTYTAG);

which would then give

<?xml version="1.0" encoding="UTF-8"?>
<foo></foo>

Just pass a node param to DOMDocument::saveXML in order to output only a specific node, without any XML declaration:

$doc = new \DOMDocument('1.0', 'UTF-8');
$doc->preserveWhiteSpace = false;
$doc->formatOutput = false;
$node = $doc->createElement('foo');

// Trimming the default carriage return char from output
echo trim($doc->saveXML($node)); 

will give

<foo/>

not containing any new line / carriage return ending char.