Description:
------------
---
From manual page: http://www.php.net/class.domdocumenttype
---
The string 

<!NOTATION image SYSTEM "%SYSTEMROOT%/paint.exe">

causes a libxml error.
Per the XML specification, a parameter entity reference cannot be recognized inside a SystemLiteral. The percent sign itself is permitted in the NOTATION.

4.4
Reference in DTD
as a reference within either the internal or external subsets of the DTD, but outside of an EntityValue, AttValue, PI, Comment, SystemLiteral, PubidLiteral, or the contents of an ignored conditional section (see 3.4 Conditional Sections).

2.3
[11]   	SystemLiteral	   ::=   	('"' [^"]* '"') | ("'" [^']* "'")

Test script:
---------------
$xmlDom = new DOMDocument();
$xmlDom->load("test.xml", LIBXML_DTDLOAD | LIBXML_DTDVALID | LIBXML_NOENT);

test.xml:
<?xml version="1.0" ?>
<!DOCTYPE root SYSTEM "test.dtd">
<root />

test.dtd:
<!ELEMENT root EMPTY>
<!NOTATION image SYSTEM "%SYSTEMROOT%/paint.exe">

Expected result:
----------------
No LIBXML error is generated and the document is correctly parsed and loaded.

Actual result:
--------------
Warning: DOMDocument::load(): PEReference: expecting ';' in file:///D:/XAMPP/htdocs/preview/tests/test.dtd, line: 2 in D:\XAMPP\htdocs\preview\tests\test.php on line 49