What is the correct xlink namesapce to use in Docbook 5?

StackOverflow https://stackoverflow.com/questions/21152687

  •  28-09-2022
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Question

If I have the following Docbook 5 XML:

<article xmlns="http://docbook.org/ns/docbook" xmlns:xl="http://www.w3.org/1999/xlink" version="5.0">
    <title>Test</title>
    <section>
        <title>LS command</title>
        <para xml:id="ls">
            This command is a synonym for <command linkend="dir">DIR</command> command.
        </para>
        <para xml:id="dir">
            This command is a synonym for <command linkend="ls">LS</command> command.
        </para>
        <para>
            <application xl:href="http://www.gnu.org/software/emacs/">Emacs</application>
        </para>
    </section>
</article>

and I attempt to validate it against the Docbook 5 DTD downloaded from here with:

xmllint --noout --dtdvalid docbook.dtd test.xml

I get the following error:

test.xml:1: element article: validity error : No declaration for attribute xmlns:xl of element article
test.xml:11: element application: validity error : No declaration for attribute href of element application

However, if I change the xl namespace to xlink, like so:

<article xmlns="http://docbook.org/ns/docbook" 
                 xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0">
    <title>Test</title>
    <section>
        <title>LS command</title>
        <para xml:id="ls">
            This command is a synonym for <command linkend="dir">DIR</command> command.
        </para>
        <para xml:id="dir">
            This command is a synonym for <command linkend="ls">LS</command> command.
        </para>
        <para>
            <application xlink:href="http://www.gnu.org/software/emacs/">Emacs</application>
        </para>
    </section>
</article>

Everything validates just fine. I got the xl namespace from the Docbook documentation here (and the example of using an article with an application that had a xref is straight from that documentation).

So why does xl fail when xlink succeeds?

Was it helpful?

Solution

The issue was actually that the DocBook 5.0 DTD specifically listed the xlink:href attribute, and any others were not valid.

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