<?xml version=“1.0”?> <!DOCTYPE doc [ <!ELEMENT doc ((a | b | c) , d)?> <!ELEMENT a (#PCDATA)> <!ELEMENT b (#PCDATA)> <!ELEMENT c (#PCDATA)> <!ELEMENT d (#PCDATA)> ]> <doc>This<d> is a valid document</d></doc>
<?xml version=“1.0”?> <!DOCTYPE doc [ <!ELEMENT doc ((a | b | c) , d)?> <!ELEMENT a (#PCDATA)> <!ELEMENT b (#PCDATA)> <!ELEMENT c (#PCDATA)> <!ELEMENT d (#PCDATA)> ]> <doc>This<d> is a valid document</d></doc>