Description:
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Calling XSLTProcessor::transformToDoc (which would be expected not to alter the source document) on a DOMDocument that has a doctype causes the doctype to be somehow "separated" from the document, so that the doctype is no longer included when writing out the original document.

A workaround is to clone the DOMDocument object before calling transformToDoc on it, but this shouldn't be necessary.

I notice that the "nextSibling" property of the DOMDocumentType object is lost during the transformation.

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Tested with PHP 5.5.10 and 5.4.24.

libxml2 Version => 2.9.0
libxslt Version => 1.1.28

Test script:
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https://gist.github.com/hubgit/9669288

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


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

Actual result:
--------------
<?xml version="1.0"?>
<article/>