<?xml version="1.0"?>
<!DOCTYPE root [
  <!ELEMENT root (a,b)>
  <!ELEMENT a EMPTY>
  <!ELEMENT b (#PCDATA|c)* >
  <!ELEMENT c ANY>
]>
<!--* illgal element in b's Mixed content *-->
<root><a/><b>
   <c></c> 
   content of b element
   <a/>
   could not have 'a' as 'b's content
</b></root>