What ISO Checks

(what a DTD could, plus)

• Check for presence of elements
  (requiring elements the DTD calls optional, like <copyright-holder>)
• Check for EMPTY elements
  (<copyright-holder> can’t be empty either)
• Counting elements in context
  (only an editor knows if 2 forewords is an error)
• Testing based on ancestors
  (only certain sections may contain a Scope or Purpose)