<!DOCTYPE persons [
<!ELEMENT persons	(Person*)>
<!ELEMENT Person	((Male, FathersName?) | (Female, MothersName?))>
<!ATTLIST Person	id ID #REQUIRED>
<!ELEMENT FathersName	(#PCDATA)>
<!ELEMENT MothersName	(#PCDATA)>
<!ELEMENT Male		EMPTY>
<!ATTLIST Male		src CDATA #IMPLIED
			alt (A|B) #REQUIRED>
<!ELEMENT Female	EMPTY>
]>
<persons/>
<Extra>
</Extra>