# Function Calls

A function call in XPath 2.0 takes the form `F ( arg1, arg2, ...)` . In general, the function name is a QName. A library of core functions is defined in the XPath 2.0 and XSLT 2.0 specifications. For details of these functions, including notes on their implementation in this Saxon release, see the Functions section. Additional functions are available (in a special namespace) as Saxon extensions: these are listed in the Extensions. Further functions may be implemented by the user, either as XSLT stylesheet functions (see xsl:function), as XQuery functions, or as Java extension functions (see the Extensibility section).

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