How to insert HTML to PHP DOMNode?

Is there any way I can insert an HTML template to existing DOMNode without content being encoded?

I have tried to do that with:

$dom->createElement('div', '<h1>Hello world</h1>');
$dom->createTextNode('<h1>Hello world</h1>');

The output is pretty much the same, with only difference that first code would wrap it in a div. I have tried to loadHTML from string but I have no idea how can I append it's body content to another DOMDocument.

In javascript, this process seems to be quite simple and obvious.