1<?xml version="1.0"?>
2<!DOCTYPE doc [
3<!ELEMENT doc ((a | b | c) , d)?>
4<!ELEMENT a (#PCDATA)>
5<!ELEMENT b (#PCDATA)>
6<!ELEMENT c (#PCDATA)>
7<!ELEMENT d (#PCDATA)>
8]>
9<doc><b>This</b><d> is a valid document</d></doc>
10