An XML Declaration

不像 SGML的Declaration 可有可无，XML 文档必须以 An XML Declaration开始。

<?xml version="1.0" standalone="no"?>

A Document Type Declaration

DocBook XML documents 需要有一个 Document Type Declaration ，虽然这并不是XML所必须。

<?xml version='1.0'?>
<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN"
                         "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd">

An Internal Subset

在一个Document Type Declaration 中，可以包含一个或者多个 Internal Subset，如：

<?xml version='1.0'?>
<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4/EN"
                         "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd" [
<!ENTITY nwalsh "Norman Walsh">
<!ENTITY chap1 SYSTEM "chap1.sgm">
<!ENTITY chap2 SYSTEM "chap2.sgm">
]>

The Document (or Root) Element

如下面的 <boot> 和 </boot> 即是该文档的唯一根元素。

<?xml version='1.0'?>
<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN"
                         "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd" [
<!ENTITY nwalsh "Norman Walsh">
<!ENTITY chap1 SYSTEM "chap1.sgm">
<!ENTITY chap2 SYSTEM "chap2.sgm">
]>
<book>...</book>