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Special characters (e.g., {+}, *, ?) appended to the name of a child element describe the expected number of occurrences of element. The + character in example 3 above declares that the child element GeneAlias must occur one or more times inside the GeneAliasCollection element. The * character in examples 1 and 5 above declares that the child element Sentence, EvidenceCode, and Roles can occur zero or more times inside the GeneEntry and Sentence elements. The ? character in example 5 above declares that the child element Comments can be absent or occur one time inside the Sentence element.

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