Demo script showing separation of doctype from source document during XSLTProcessor::transformToDoc

doctype-test.php

<?php

// prepare the XSL processor
$stylesheet = new DOMDocument;
$stylesheet->loadXML('<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"/>');

$processor = new XSLTProcessor;
$processor->importStylesheet($stylesheet);

// load the XML (with a doctype)
$doc = new DOMDocument;
$doc->loadXML('<?xml version="1.0"?>
<!DOCTYPE article PUBLIC "-//example//EN" "http://example.org/dtd">
<article/>');

printf("Doctype ID: %s\n", $doc->doctype->publicId); // Doctype ID: -//example//EN
printf("Next sibling: %s\n\n", $doc->doctype->nextSibling->nodeName); // 'article'

// write out the original document (has doctype)
print $doc->saveXML();

/*
<?xml version="1.0"?>
<!DOCTYPE article PUBLIC "-//example//EN" "http://example.org/dtd">
<article/>
*/

// transform the document (transformToDoc or transformToXML)
// this is where the doctype gets unexpectedly separated
// normally $output would be used, but is ignored here
$output = $processor->transformToDoc($doc);

// the doctype is still there, but has no nextSibling
printf("\nDoctype ID: %s\n\n", $doc->doctype->publicId); // Doctype ID: -//example//EN
//printf("Next sibling: %s\n", $doc->doctype->nextSibling->nodeName); // no nextSibling

// write out the original document again (no doctype)
print $doc->saveXML();

/*
<?xml version="1.0"?>
<article/>
*/