The master document file, in our example XD-999.xml, is a short file which has, besides some general document information, some include statements. The following shows a simple form of this file. Everthing that's between the <bookinfo> ... </bookinfo> whithin the original file shouldn't bother us at the moment. The same is true for the <index ...> </index>

<?xml version="1.0" encoding='utf-8'?>
<!-- jEdit buffer-local properties: -->
<!-- :indentSize=2:noTabs=true: -->
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"[
 <!ENTITY mg_sample_section SYSTEM "mg_sample_section.xml">
 <!ENTITY sample SYSTEM "sample.xml">
 <!ENTITY mg_intro SYSTEM "mg_intro.xml">
 <!ENTITY mg_sample_chapter SYSTEM "mg_sample_chapter.xml">
 <!ENTITY installation SYSTEM "installation.xml">
 <!ENTITY % glossary SYSTEM "../glossary.ent">
 %glossary;
]>
<book lang="en"> &mg_intro;
 &sample;
 &mg_sample_chapter;
 &installation; <index role="with_index" id="TheVeryLastPage">
 </index>
</book>

For the startup DocBook writer the only interest here are the include statements. We include files as file entities

The file entities are included in the normal entity way.

&sample;

What is now included by the first file? It's just exactly this chapter, the lines you just read. To make things a little easier, we will continue with the second include statement, which includes the docbook/sample.xml. Within this chapter we will explain the most common DocBook tags.