3 <!ELEMENT a (b | (c, d)* | (e, f)+ | g?)>
4 <!ELEMENT b (#PCDATA | a)*>
11 <!ATTLIST a u CDATA #IMPLIED
14 x NOTATION (n1|n2) "n1"
17 <!NOTATION n1 SYSTEM "/bin/n1-processor">
18 <!NOTATION n2 SYSTEM "/bin/n2-processor">
20 <!ENTITY u1 SYSTEM "file-u1" NDATA n1>
21 <!ENTITY u2 SYSTEM "file-u2" NDATA n2>
26 <a u="1" w="q" x="n2">