Home >Online Product Documentation >Table of Contents >Calling Functions in Queries
The XPath processor provides many functions that you can call in a query. This section provides some examples to give you a sense of how functions in queries work. Many subsequent sections provide information about invoking functions in queries. For a complete list of the functions you can call in a query, see XPath Functions Quick Reference.
Following is a query that returns a number that indicates how many book elements are in the document:
book
count(//book)
In format descriptions, a question mark that follows an argument indicates that the argument is optional. For example:
string substring(string, number, number?)
This function returns a string. The name of the function is substring. This function takes two required arguments (a string followed by a number) and one optional argument (a number).
substring
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