<?xml version="1.0"?>

<!DOCTYPE circle
[
   <!ELEMENT circle (position)>
   <!ATTLIST circle
          diameter CDATA #REQUIRED>

   <!ELEMENT position EMPTY>
   <!ATTLIST position
          x CDATA #REQUIRED
          y CDATA #REQUIRED>
]>

<circle diameter="30">
  <position x="30" y="50"/>
</circle>

