l<!DOCTYPE book
l [ <!ELEMENT book (title, subtitle?, author+, info) >
l <!ATTLIST book id
CDATA #REQUIRED >
l <!ELEMENT title PCDATA >
l <!ELEMENT subtitle PCDATA >
l <!ELEMENT author PCDATA >
l <!ELEMENT info (key*, isbn) >
l <!ELEMENT key PCDATA >
l <!ELEMENT isbn
PCDATA >
l ]>