xsltproc is installed on macOS Sierra and the dumpextensions switch is very handy.

$ xsltproc -dumpextensions
Registered XSLT Extensions
--------------------------
Registered Extension Functions:
{http://exslt.org/math}cos
{http://exslt.org/sets}difference
{http://exslt.org/sets}has-same-node
{http://exslt.org/strings}tokenize
{http://exslt.org/dates-and-times}date-time
{http://exslt.org/dates-and-times}minute-in-hour
{http://exslt.org/dates-and-times}week-in-month
{http://exslt.org/math}lowest
{http://exslt.org/dates-and-times}add
{http://exslt.org/dates-and-times}date
{http://exslt.org/dates-and-times}month-abbreviation
{http://icl.com/saxon}expression
{http://exslt.org/dynamic}evaluate
{http://exslt.org/math}min
{http://exslt.org/math}abs
{http://exslt.org/math}sin
{http://exslt.org/math}acos
{http://exslt.org/strings}padding
{http://exslt.org/dates-and-times}month-in-year
{http://exslt.org/dates-and-times}sum
{http://exslt.org/common}object-type
{http://exslt.org/math}power
{http://exslt.org/strings}decode-uri
{http://exslt.org/dates-and-times}day-name
{http://exslt.org/dates-and-times}duration
{http://exslt.org/dates-and-times}seconds
{http://exslt.org/dates-and-times}add-duration
{http://exslt.org/dates-and-times}day-abbreviation
{http://exslt.org/dates-and-times}day-in-week
{http://exslt.org/dates-and-times}leap-year
{http://exslt.org/dates-and-times}time
{http://icl.com/saxon}line-number
{http://exslt.org/dynamic}map
{http://exslt.org/math}highest
{http://exslt.org/math}atan2
{http://exslt.org/dates-and-times}day-in-month
{http://exslt.org/dates-and-times}difference
{http://exslt.org/math}asin
{http://exslt.org/sets}leading
{http://exslt.org/strings}split
{http://exslt.org/strings}replace
{http://icl.com/saxon}evaluate
{http://exslt.org/common}node-set
{http://exslt.org/math}max
{http://exslt.org/math}constant
{http://exslt.org/math}sqrt
{http://exslt.org/math}atan
{http://exslt.org/math}exp
{http://exslt.org/sets}distinct
{http://exslt.org/sets}trailing
{http://exslt.org/dates-and-times}day-in-year
{http://exslt.org/math}random
{http://exslt.org/math}tan
{http://exslt.org/sets}intersection
{http://exslt.org/strings}encode-uri
{http://exslt.org/strings}align
{http://exslt.org/dates-and-times}hour-in-day
{http://exslt.org/dates-and-times}second-in-minute
{http://exslt.org/dates-and-times}year
{http://icl.com/saxon}eval
{http://exslt.org/math}log
{http://exslt.org/strings}concat
{http://exslt.org/dates-and-times}day-of-week-in-month
{http://exslt.org/dates-and-times}month-name
{http://exslt.org/dates-and-times}week-in-year
{http://icl.com/saxon}systemId
{http://xmlsoft.org/XSLT/}test

Registered Extension Elements:
{http://exslt.org/common}document
{http://exslt.org/functions}result
{http://xmlsoft.org/XSLT/}test

Registered Extension Modules:
http://icl.com/saxon
http://xmlsoft.org/XSLT/
http://exslt.org/functions