<?xml version="1.0"?>
<!DOCTYPE DOCUMENT [
   <!ELEMENT DOCUMENT (P*)>
   <!ELEMENT P (#PCDATA)>
   <!ATTLIST P PNUMBER ID #REQUIRED>
]>
<DOCUMENT>
  <P PNUMBER="p1">The quick brown fox</P>
  <P PNUMBER="p2">The quick brown fox</P>
</DOCUMENT>
