Be careful when using this for partial HTML. This will only take complete HTML documents with at least an HTML element and a BODY element. If you are working on partial HTML and you fill in the missing elements around it and don't specify in META elements the character encoding then it will be treated as ISO-8859-1 and will mangle UTF-8 strings. Example:
<?php
$body = getHtmlBody();
$doc = new DOMDocument();
$doc->loadHtml("<html><body>".$body."</body></html>");
?>
<?php
$body = getHtmlBody();
$doc = new DOMDocument();
$doc->loadHtml("<html><head><meta charset=\"UTF-8\"><meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\"></head><body>".$body."</body></html>");
?>