XML DTDs - slide "Multiple Children"

a+ - One or more ocurrences of a
<!ELEMENT BOOK (CHAPTER)+>
a* - Zero or more ocurrences of a
<!ELEMENT List (Object)*>
a? - a or nothing
<!ELEMENT Table (plate)?>
a, b - a followed by b
<!ELEMENT SUM (op1, op2)>
a | b - a or b but not both
<!ELEMENT POINT (COORDINATES | POLAR)>
(expression) - expression treated as a unit
<!ELEMENT CHAPTER (INTRODUCTION, (P | QUOTE | NOTE)*, DIV*)>