1 <!DOCTYPE doc

     2 [

     3 <!ELEMENT doc (a|b)*>

     4 <!ELEMENT a ANY>

     5 <!ELEMENT b ANY>

     6 <!NOTATION a SYSTEM "a">

     7 <!ATTLIST a att (a|b) #IMPLIED>

     8 <!ATTLIST b att NOTATION (a|b) #IMPLIED>

     9 <!NOTATION b SYSTEM "b">

    10 ]>

    11 <doc/>