Question

I thought that I was properly creating an xml document in my php script from a mysql query, but I am not getting an xml document in return (with no php errors to help me) even though the mysql query works!

    <?php
    ...
    $result = $mysqli->query($sql);
    if ($result) {       //this query works, but no xml document produced as a result
    $d = new DOMDocument();
    $books = $d->createElement('hey');
    $hey->setAttribute('check','The Adventures of Tom Sawyer');
    $d->appendChild($books);
    $d->appendChild($hey);
    $d->appendChild($books);
    echo $d->saveXML();
}
    ?>

Answer 1

$d->setAttribute('check','The Adventures of Tom Sawyer');

$d “is” the DOMDocument object and there is no DOMDocument::setAttribute() method.
Either use DOMElement::setAttribute() or DOMDocument::createAttribute()

if ($result) {
    $d = new DOMDocument();
    $books = $d->createElement('hey');
    $books->setAttribute('check','The Adventures of Tom Sawyer');
    $d->appendChild($books);
    echo $d->saveXML();
}