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# XSLT Functions * * * XQuery 1.0, XPath 2.0, and XSLT 2.0 share the same function library. * * * ## XSLT Functions XSLT contains over 100 built-in functions. These functions are used for string values, numeric values, date and time comparisons, node and QName operations, sequence operations, boolean values, and more. The default prefix for the function namespace is fn. The URI for the function namespace is: http://www.w3.org/2005/xpath-functions **Tip:** Functions are often called with the fn: prefix, such as fn:string(). However, since fn: is the default namespace prefix, the function name does not need to use a prefix when called. [You can access the reference manual for all built-in XSLT 2.0 functions in our XPath tutorial.](#) Additionally, the built-in XSLT functions are listed below: | Name | Description | | --- | --- | | [current()](#) | Returns the current node. | | [document()](#) | Used to access nodes in external XML documents. | | [element-available()](#) | Tests whether the XSLT processor supports the specified element. | | [format-number()](#) | Converts a number to a string. | | [function-available()](http://www.runGeekTime.com/xsl/func-functionavailable.html) | Tests whether the XSLT processor supports the specified function. | | [generate-id()](#) | Returns a string value that uniquely identifies the specified node. | | [key()](#) | Returns a node set by using the index number specified by the element. | | [system-property()](#) | Returns the value of a system property. | | [unparsed-entity-uri()](#) | Returns the URI of an unparsed entity. |