1  <!ENTITY % a SYSTEM "http://example.org/a/a.dtd">
2  %a;
3  <!ENTITY % b SYSTEM "http://example.org/b/b.dtd">
4  %b;
5  <!ENTITY % c SYSTEM "http://example.org/c/c.dtd">
6  %c;
7  <!ELEMENT abc (a, b, c)>