test/dtd9 - third_party/libxml2 - Git at Google

 <!DOCTYPE doc [
 <!ELEMENT doc ((a | b | c) , d)?>
 <!ELEMENT a (#PCDATA)>
 <!ELEMENT b (#PCDATA)>
 <!ELEMENT c (#PCDATA)>
 <!ELEMENT d (#PCDATA)>
 ]>
 <doc><b>This</b><d> is a valid document</d></doc>
	<!DOCTYPE doc [
	<!ELEMENT doc ((a \| b \| c) , d)?>
	<!ELEMENT a (#PCDATA)>
	<!ELEMENT b (#PCDATA)>
	<!ELEMENT c (#PCDATA)>
	<!ELEMENT d (#PCDATA)>
	]>
	<doc><b>This</b><d> is a valid document</d></doc>