1 <?xml version="1.0"?> 2 <!DOCTYPE doc [ 3 <!ELEMENT doc ((a | b | c) , d)?> 4 <!ELEMENT a (#PCDATA)> 5 <!ELEMENT b (#PCDATA)> 6 <!ELEMENT c (#PCDATA)> 7 <!ELEMENT d (#PCDATA)> 8 ]> 9 <doc><b>This</b><d> is a valid document</d></doc> 10
