Check in the libxslt roll script.

third_party/libxslt/src/libexslt/date.c

 /*
  * date.c: Implementation of the EXSLT -- Dates and Times module
  *
  * References:
  *   http://www.exslt.org/date/date.html
  *
  * See Copyright for the status of this software.
  *
  * Authors:
  *   Charlie Bozeman <cbozeman@HiWAAY.net>
@@ skipping 3891 matching lines @@
                                    (const xmlChar *) EXSLT_DATE_NAMESPACE,
                                    exsltDateWeekInYearFunction)
         && !xmlXPathRegisterFuncNS(ctxt,
                                    (const xmlChar *) "year",
                                    (const xmlChar *) EXSLT_DATE_NAMESPACE,
                                    exsltDateYearFunction)) {
         return 0;
     }
     return -1;
 }