Chaining Catalogs

Catalogs can be chained together. For example, consider /etc/catalog.xml:

<?xml version='1.0'?>
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">

  <nextCatalog catalog="/usr/share/docbook/4.2/catalog.xml"/>
  <nextCatalog catalog="/usr/share/html/4.01/catalog.xml"/>
  <nextCatalog catalog="/usr/share/entities/8879.1986/catalog.xml"/>

</catalog>