Element: Instance Quantities
To specify the number of times a child element can appear in an element, the instance quantities in the following table can be appended with the child element.

Instance Quantity

Description

* (asterisk)

Declares that an element can occur zero or more times. The following example indicates that the child element to can appear any number of times in the scope of the mail element:
    <!ELEMENT mail (to*, from)>

+ (plus)

Declares that an element can occur one or more times. The following example indicates that the child element from can appear one or more times in the scope of the mail element:
    <!ELEMENT mail (to, from+)>

? (question mark)

 

Declares that an element can occur zero or maximum of one time. The following example indicates that a mail element can have zero or one subject:
    <!ELEMENT mail(subject?)>

 

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