<refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          xmlns:src="http://nwalsh.com/xmlns/litprog/fragment"
          xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
          version="5.0" xml:id="prefer.internal.olink">
<refmeta>
<refentrytitle>prefer.internal.olink</refentrytitle>
<refmiscinfo class="other" otherclass="datatype">boolean</refmiscinfo>
</refmeta>
<refnamediv>
<refname>prefer.internal.olink</refname>
<refpurpose>Prefer a local olink reference to an external reference</refpurpose>
</refnamediv>

<refsynopsisdiv>
<src:fragment xml:id="prefer.internal.olink.frag">
<xsl:param name="prefer.internal.olink" select="0"/>
</src:fragment>
</refsynopsisdiv>

<refsection><info><title>Description</title></info>

<para>If you are re-using XML content modules in multiple documents,
you may want to redirect some of your olinks.  This parameter
permits you to redirect an olink to the current document.
</para>

<para>For example: you are writing documentation for a  product, 
which includes 3 manuals: a little installation
booklet (booklet.xml), a user 
guide (user.xml), and a reference manual (reference.xml).
All 3 documents begin with the same introduction section (intro.xml) that 
contains a reference to the customization section (custom.xml) which is 
included in both user.xml and reference.xml documents.
</para>

<para>How do you write the link to custom.xml in intro.xml
so that it is interpreted correctly in all 3 documents?</para>
<itemizedlist>
<listitem><para>If you use xref, it will fail in user.xml.</para>
</listitem>
<listitem><para>If you use olink (pointing to reference.xml),
the reference in user.xml  
will point to the customization section of the reference manual, while it is 
actually available in user.xml.</para>
</listitem>
</itemizedlist>

<para>If you set the <parameter>prefer.internal.olink</parameter>
parameter to a non-zero value, then the processor will
first look in the olink database
for the olink's <tag>targetptr</tag> attribute value
in document matching the <parameter>current.docid</parameter>
parameter value.  If it isn't found there, then
it tries the document in the database
with the <tag>targetdoc</tag>
value that matches the olink's <tag>targetdoc</tag>
attribute.
</para>

<para>This feature permits an olink reference to resolve to
the current document if there is an element
with an id matching the olink's <tag>targetptr</tag>
value.  The current document's olink data must be
included in the target database for this to work.</para>

<caution>
<para>There is a potential for incorrect links if
the same <tag>id</tag> attribute value is used for different
content in different documents.
Some of your olinks may be redirected to the current document
when they shouldn't be.  It is not possible to control
individual olink instances.</para>
</caution>

</refsection>
</refentry>