A valid example

<?xml version="1.0"?>

<!DOCTYPE PARENT [

<!ELEMENT PARENT (CHILD*)>

<!ELEMENT CHILD (MARK?,NAME+)>

<!ELEMENT MARK EMPTY>

<!ELEMENT NAME (LASTNAME+,FIRSTNAME+)*>

<!ELEMENT LASTNAME (#PCDATA)>

<!ELEMENT FIRSTNAME (#PCDATA)>

<!ATTLIST MARK

NUMBER ID #REQUIRED

LISTED CDATA #FIXED "yes"

TYPE (natural|adopted) "natural">

<!ENTITY STATEMENT "This is well-formed XML">

]>

<PARENT>

&STATEMENT;

<CHILD>

<MARK NUMBER="1" LISTED="yes" TYPE="natural"/>

<NAME>

<LASTNAME>child</LASTNAME>

<FIRSTNAME>second</FIRSTNAME>

</NAME>

</CHILD>

</PARENT>