DOMElement cloning and appending: 'Wrong Document Error'

Use DOMDocument->importNode to import the node into the other document before adding it to the DOM.

You'll have to append the result of the importNode method to the DOM. Keep in mind that the method could return false when it cannot be imported

if ($importedNode = $doc2->importNode($root->cloneNode())) {    $root2->appendChild($importedNode);}

If you need to import the node, all of it's child nodes (resursively) and/or the node's attributes use the optional second parameter deep:

if ($importedNode = $doc2->importNode($root->cloneNode(), true)) {    $root2->appendChild($importedNode);}

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