<?xml version='1.0' ?>
<!DOCTYPE test  [
<!ELEMENT test (#PCDATA | inner)*>
<!ELEMENT inner (#PCDATA)>
<!ATTLIST inner attr CDATA #IMPLIED>
<!ENTITY t1 "t2=&t2;...">
<!ENTITY t2 "t3=&t3;...">
<!ENTITY t3 "t1=&t1;...">
]>
<test
  ><!Error: Recursive substitution of RefEntity "t2"></test>