为什么这些Xpath元素不是一个数组？

So this works fine in a foreach which I thought meant $elements was an array...

$DOM = new DOMDocument(); 
$DOM->loadHTML($content);
$xpath = new DOMXPath($DOM);
$elements= $xpath->query('//li');

foreach($elements as $element){
    $newdoc = new DOMDocument();
    $cloned = $element->cloneNode(TRUE);
    $newdoc->appendChild($newdoc->importNode($cloned,TRUE));
    $lis .= $newdoc->saveHTML();
}

But this

if ($elements[0]) {
    echo $elements[0]->nodeValue;   
}

Gives Cannot use object of type DOMNodeList as array

The foreach() there is not a class method so why does it function on the DOMNodeList as if it were an array when apparently it is not one?

It's all perfectly explained in the php documentation: the DOMNodeList class implements the Iterator interface, which allows the use of foreach on objects of that class.

Note that you can use the item method to access any elements of the list by index:

$elements->item(0)->nodeValue

My guess is that php's foreach function knows how to iterate objects besides arrays, but in terms of getting an array from the DomNodeList, use this:

$arr = [];
foreach ($elements as $element) {
    $arr[] = $element;
}
echo $arr[0]->nodeValue;