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<xi:fallback> XInclude Fallback

To quote the XInclude Recommendation, “the <xi:fallback> element appears as a child of an <xi:include> element. It provides a mechanism for recovering from missing resources. When a resource error is encountered, the <xi:include> element is replaced with the contents of the <xi:fallback> element. If the <xi:fallback> element is empty, the <xi:include> element is removed from the result”.

Usage/Remarks

Since it is not the business of this Tag Set to specify processing, the <xi:fallback> element will default to #PCDATA, but the parameter entity %fallback-model; can be redefined in the customization of any user organization that desires a different fallback result.
Attribute

Namespaces

xmlns:xi (fixed value = http://www.w3.org/2001/XInclude)
Models and Context
May be contained in
<xi:include>
Description
Text, numbers, or special characters
Content Model
<!ELEMENT  xi:fallback  %fallback-model;                             >
Expanded Content Model

(#PCDATA)

Tagged Sample

Designating the “back-up” link for a file as EMPTY (i.e., if the primary XInclude link encounters an error, the file should not appear on output) 

<book 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:xi="http://www.w3.org/2001/XInclude"
  xmlns:mml="http://www.w3.org/1998/Math/MathML"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  dtd-version="2.1"
  xml:lang="en">
 <book-meta>...</book-meta>

 <!-- ===== Front Matter (Narrative Content) ===== -->
 <front-matter>
  <!-- Dedication -->
  <xi:include  href="bits-book-part4.xml"
    xmlns:xi="http://www.w3.org/2001/XInclude"></xi:include>
  ...
 </front-matter>

 <!-- =============== Body Matter (Content) =========== -->
 <book-body>
  <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="bits-book-part1.xml">
   <xi:fallback/>
  </xi:include>
  <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="bits-book-part2.xml"></xi:include>
  <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="bits-book-part3.xml"></xi:include>
 </book-body>

 <!-- =============== Back Matter (Ancillary) ======= -->
 <book-back>
  <ack>...</ack>
  ...
 </book-back>

</book>