Description:
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I guess this may not be a bug but I can find no information about how to import an XML with a DTD declaration (<!DOCTYPE...) and have the resulting XML still contain the declaration when I use the asXML method.  All I get is the file with the declaration removed.  I have tried LIBXML_DTDLOAD, LIBXML_DTDATTR and they don't seem to help.

On a related note when I set an element using simplexml and it includes an '&' ans part of an entity reference (i.e. &M;) it gets converted to '&amp;'. How can I stop that?

Test script:
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$exptml= simplexml_load_file('http://chalk.coas.unf.edu/eureka/files/templates/tmpl_chm.xml');
echo $exptml->asXML();

Expected result:
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<?xml version="1.0" encoding="UTF-8"?>
<!-- Example Chemical - ExptML v0.1 SJC 4/7/11 -->
<!DOCTYPE ExptML SYSTEM "http://chalk.coas.unf.edu/eureka/files/exptml/exptml_entities.dtd">
<chemical id="pid" xmlns="urn:exptml:schema:draft:0.1"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:unitsml="urn:oasis:names:tc:unitsml:schema:xsd:UnitsMLSchema-1.0"
	xsi:schemaLocation="urn:exptml:schema:draft:0.1 http://chalk.coas.unf.edu/eureka/files/exptml/exptml_chemical.xsd" version="0.1">
<name>Chemical name</name>
...
</chemical>


Actual result:
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<?xml version="1.0" encoding="UTF-8"?>
<!-- Example Chemical - ExptML v0.1 SJC 4/7/11 -->

<chemical id="pid" xmlns="urn:exptml:schema:draft:0.1"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:unitsml="urn:oasis:names:tc:unitsml:schema:xsd:UnitsMLSchema-1.0"
	xsi:schemaLocation="urn:exptml:schema:draft:0.1 http://chalk.coas.unf.edu/eureka/files/exptml/exptml_chemical.xsd" version="0.1">
<name>Chemical name</name>
...
</chemical>