<!ELEMENT sectors (sector+)>
<!ELEMENT sector (disc|rectangle|polygon|union|intersection)>
<!ELEMENT union (disc|rectangle|polygon|union|intersection)+>
<!ELEMENT intersection (disc|rectangle|polygon|union|intersection)+>
<!ELEMENT disc (point)>
<!ELEMENT rectangle (point,point)>
<!ELEMENT polygon (point,point,point+)>
<!ELEMENT point EMPTY>

<!ATTLIST sectors>
<!ATTLIST union>
<!ATTLIST intersection>
<!ATTLIST rectangle>

<!ATTLIST sector
  name CDATA #REQUIRED
>

<!ATTLIST disc
  radius CDATA #REQUIRED
>

<!ATTLIST point
  pos CDATA #REQUIRED
>
