PHP Xpath不返回“实时”节点列表

Question

Sometimes it seems that the DOMNodeList returned isn't live.

It IS live when using access like childNodes

 $children=$doc->getElementsByTagName('body')->item(0)->childNodes;
 echo $children->length;  //7
 $children->item(0)->parentNode->removeChild($children->item(0));

  echo $children->length;  //6! list is live! 

But other times the list is NOT live...

$xpath=new DOMXPath($doc);
$nodes=$xpath->query("//p");

echo $nodes->length; // 7
$nodes->item(0)->parentNode->removeChild($nodes->item(0));
echo $nodes->length; // still 7? Not live. 

XPath seems to be the major culprit. But why return a DOMNodeList if it isn't live? Why not just an array at that point?