EXSLT is an extension library for XSLT, mainly for XSLT 1.0. It includes functionality to provide missing language features such as set operations, node-set coercion, date methods, math functions, and type checking. Note that with XSLT 2 and 3 none of these are usually needed as the languages themselves and/or their underlying standards like the XPath 2 or 3 type system or the XPath 2 or 3 function library have all and more integrated and standardised.
The EXSLT project defines the namespaces for the library. To make use of one of these functions or extension elements, the appropriate namespace must be declared on the xsl:stylesheet element and your processor must have support for the particular function or extension element.
