Template:DoctypeDisallowed
From Documentation
DOCTYPE restriction
Since 10.0.0
Starting from ZK 10, the xml parser used by ZK declares disallow-doctype-decl to true.
This prevents the use of DOCTYPE declaration in xml files, such as zk.xml, lang-addon.xml, config. xml, etc.
This is a security measure to prevent XXE attacks using <!DOCTYPE ...> as vector.