result/valid/t10.xml

<?xml version="1.0" standalone="yes"?>
<!DOCTYPE root [
<!ELEMENT root (cont1 , (cont1 , cont2?)+)>
<!ELEMENT cont1 EMPTY>
<!ELEMENT cont2 EMPTY>
]>
<root>
  <cont1/>
  <cont1/>
  <cont1/>
  <cont1/>
</root>