Description:
------------
I am trying to validate a DocBook having namest and nameend attribute in entry element with RelexNg (http://docbook.org/xml/5.0/rng/docbook.rng). I am using following php code for validation. It is displaying errors in xml file but xml file (DocBook) is valid. I have checked this XMl file on some tool whixh says it valid like oXygen.
 
$dom_xml = new DomDocument;
$dom_xml->load("textExample.xml");
                     
if ($dom_xml->relaxNGValidate("docbook.rng") )
{
               echo "Good\n";
}
else
{
    echo $php_errormsg . "\n";
}

I am attaching sample DocBook in the mail.

Reproduce code:
---------------
XML File (DocBook) file:

<?xml version="1.0" encoding="UTF-8"?>
<book xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0">
    <info>
        <title>Book Template Title</title>
        <author>
            <orgname>Organization Name</orgname>
            <address>
                <city>City</city>
                <street>Street</street>
                <postcode>000000</postcode>
                <country>Country</country>
            </address>
            <email>user@example.com</email>
        </author>
    </info>
    <part>
        <title>First Part</title>
        <subtitle>Subtitle of First Part</subtitle>
        <chapter>
            <title>Chapter Title</title>
            <subtitle>Subtitle of Chapter</subtitle>
             <table frame="none">
                    <title>Table1</title>
                    <tgroup cols="2">
                        <colspec colname="c1" colnum="1"/>
                        <colspec colname="c2" colnum="2"/>
                        <thead>
                            <row>
                                <entry namest="c1" nameend="c2">Header 1</entry>
                            </row>
                        </thead>
                        <tbody>
                            <row>
                                <entry/>
                                <entry/>
                            </row>
                            <row>
                                <entry/>
                                <entry/>
                            </row>
                            <row>
                                <entry/>
                                <entry/>
                            </row>
                        </tbody>
                    </tgroup>
               </table>
            <sect1>
                <title>Section1 Title</title>
                <subtitle>Subtitle of Section 1</subtitle>
                <para>Text</para>
            </sect1>
        </chapter>
    </part>
</book>

Expected result:
----------------
It should be Good.

Actual result:
--------------
Displaying Errors.