EXSLT Extensions
EXSLT was an initiative to define a standardized set of extension functions and extension elements that can be used across different XSLT processors. Most of its activity was in the era of XSLT 1.0, and many of the functions that were defined are no longer needed in an XSLT 2.0 environment, because there are suitable facilities in the standard. Nevertheless, Saxon implements some of these functions for compatibility reasons.
Saxon supports the EXSLT modules Common, Math, Sets, DatesAndTimes, and Random. These functions are available both in XSLT and in XQuery. The full list of EXSLT extension functions implemented is:

common (namespace http://exslt.org/common): nodeset(), objecttype(). These are retained for compatibility with XSLT 1.0 stylesheets.

math (namespace http://exslt.org/math): abs(), acos(), asin(), atan(), atan2(), constant(), cos(), exp(), highest(), log(), lowest(), max(), min(), power() [see below], random(), sin(), sqrt(), tan(). The random() function is also implemented, but it doesn't work well: since it is not a pure function, Saxon sometimes optimizes it so that successive calls all return the same value. The random:randomsequence() function is preferable.

sets (namespace http://exslt.org/sets): difference(), intersection(), leading(), trailing(), hassamenode()

datesandtimes (namespace http://exslt.org/datesandtimes): add(), addduration(), date(), datetime(), dayabbreviation(), dayinmonth(), dayinweek(), dayinyear(), dayname(), dayofweekinmonth(), difference(), duration(), hourinday(), leapyear(), minuteinhour(), monthabbreviation(), monthinyear(), monthname(), secondinminute(), seconds(), sum(), time(), weekinmonth(), weekinyear(), year().

random (namespace http://exslt.org/random): randomsequence()
These extensions are available in SaxonPE and SaxonEE "out of the box". They are not available in SaxonHE.
The source code is available in the saxonresources download, package net.sf.saxon.option.exslt
. The code
is available under the Mozilla Public License version 2.0.
There are some known restrictions and local interpretations:

In the
set:leading()
andset:trailing()
functions, Saxon does not implement the rule "If the first node in the second node set is not contained in the first node set, then an empty node set is returned." This rule prevents a pipelined implementation. Saxon returns all nodes that precede/follow the first/last node of the second nodeset in document order, whether or not the two nodesets intersect.
EXSLT extensions that overlap XSLT 2.0 functionality have sometimes been retained in cases where they have no
impact on the Saxon core code, but in cases (such as func:function
) where the semantics are
inconveniently different from XSLT 2.0, they have been withdrawn.
The function math:power()
has been extended from the EXSLT definition to handle numeric data
types other than xs:double. The result will now be an xs:integer if the first argument is an xs:integer and
the second argument is a nonnegative xs:integer. Otherwise, the result will be an xs:decimal if the first argument is
an xs:decimal or xs:integer, and the second argument is a whole number (a number of any data type that is equal
to some integer). In other cases the arguments are converted to xs:double and the result is an xs:double.
The specifications of the EXSLT dateandtime handling functions have little to say about timezones. Saxon generally handles inputs with or without a timezone, and uses the XPath 2.0 concept of implicit timezone to interpret the meaning of dates/times without a timezone. The current date and time used by EXSLT functions is the same as that used by the XPath 2.0 currentdateTime() function.