1 <?xml version='1.0' encoding='UTF-8'?>
 2 
 3 <!ELEMENT task (description,subtasks?,prerequisites?)>
 4 <!ELEMENT description       (#PCDATA)>
 5 <!ELEMENT subtasks          (task)+>
 6 <!ELEMENT prerequisites     EMPTY>
 7 
 8 <!ATTLIST task
 9     deadline     CDATA              #IMPLIED
10     priority     (low|medium|high)  #REQUIRED
11     id            ID                #REQUIRED
12     >
13 <!ATTLIST prerequisites
14     prereqs             IDREFS      #REQUIRED
15     >
16 
17