<?xml version='1.0' encoding='UTF-8'?>

<!ELEMENT book (title, author, character*)>
<!ATTLIST book isbn CDATA #REQUIRED>

<!ELEMENT title (#PCDATA)>

<!ELEMENT author (#PCDATA)>

<!ELEMENT character (name, friend-of?, since?, qualification?)>

<!ELEMENT name (#PCDATA)>
<!ELEMENT friend-of (#PCDATA)>
<!ELEMENT since (#PCDATA)>
<!ELEMENT qualification (#PCDATA)>
