<!DOCTYPE subject SYSTEM "/usr/share/xml/docbook/schema/dtd/4.5/docbookx.dtd" [
...
]>
			
			

			
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V5.0//EN" "http://www.oasis-open.org/docbook/xml/5.0b5/dtd/docbook.dtd" [
...
]>