A space separates the two characters. The letter o means that the tag is optional. The DTD for Helptag 1.3 requires start and end tags for every element. It defines the sequence of elements and, if applicable, the number of occurrences that may occur. It can be repeated.
Element can appear zero or one time.
It is called an inclusion. Parentheses are used to enclose one or more elements. It is called an exclusion. Parentheses are used to enclose one or more elements. Each example contains a word description for the element declaration provided.