no answer == validated OK?
If you are validating against an HTML doctype then this does permit certain elements to be left open (they will be closed automatically - but not necessarily where you expect?) - so you won't necessarily get a validation error. However, if you are validating against an XHTML doctype then all your elements must be closed in the source, so the validator will catch any unclosed elements in this instance.
Do you think there is a mistake because it doesn't look as you expect?