<!ELEMENT something (itema,itemb)> <!ELEMENT itema (x1?,x2?)> <!ELEMENT x1 (#PCDATA)> <!ELEMENT x2 (#PCDATA)> <!ELEMENT itemb (#PCDATA)>this xml document is valid:
<?xml version="1.0"?> <!DOCTYPE something SYSTEM "something.dtd"> <something> <itema> <x1>Test</x1> <x2>1</x2> </itema> <itemb>more junk</itemb> </something>this xml document is invalid because things are out of order:
<?xml version="1.0"?> <!DOCTYPE something SYSTEM "something.dtd"> <something> <itemb>one error</itemb> <itema> <x2>and another</x2> <x1>error</x1> </itema> </something>