Merkede seksjoner forutsetter et 'internt subsett':
<!DOCTYPE book PUBLIC"-//OASIS//DTD DocBook V4.1//EN"[ <!ENTITY % db-oracle "IGNORE"> <!ENTITY % db-ibmdb2 "IGNORE"> <!ENTITY % appserv-websphere "IGNORE"> <!ENTITY % appserv-silverstream "IGNORE"> <!ENTITY % os-mswin "IGNORE"> <!ENTITY % os-solaris "IGNORE"> <!ENTITY % print "IGNORE"> <!ENTITY % online "IGNORE"> <!ENTITY conceptsoverview.sgm SYSTEM "concepts_with_cond.sgm"> ]> . . . <book> <title> Installing on <![%os-mswin;[Microsoft Windows NT/2000]]><![%os-solaris;[Solaris]]> servers running <![%db-oracle;[Oracle]]><![%db-ibmdb2;[IBM DB2]]> database and < ![%appserv-silverstream;[SilverStream]]><![%appserv-websphere;[IBM WebSphere]]> application server </title> <chapter> . . . </chapter> </book>