1.2. Notation of quantifier (cardinality of the data item)

The following table describes the possible forms of the quantifier:

occurs required exactly one occurrence (occurs 1)
occurs optional zero or one occurrence (occurs 0..1)
occurs ?        zero or one occurrence (occurs 0..1)
occurs *        unlimited occurrence (occurs 0..*)
occurs +        one or more occurrences (occurs 1..*)

Explicit forms of the quantifier:

occurs n     exactly n occurrences
occurs m..n  minimum m occurrences, maximum n occurrences
occurs m..*  minimum m occurrences, maximum unlimited

The keyword "occurs" may by omitted. Following notations of the quantifier are equivalent:  "occurs 10"  and   "10".

Note that since the default value of the quantifier is " required ", its entry can be omitted. E.g:
  ISBN="required int(10000000, 999999999)"
can be written as:
  ISBN="int(10000000, 999999999)"