DTD Customization Layer

In general, DTD customization layers look like this:

<!-- Turn off markup -->

<!-- Redefine parameter entities -->

<!-- include the base DTD -->
<!ENTITY % docbook PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
          "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd"
>
%docbook;

<!-- Redefine elements/attributes -->