diff --git a/src/lang/date.js b/src/lang/date.js
index b50a92b..e67338b 100644
--- a/src/lang/date.js
+++ b/src/lang/date.js
@@ -8,6 +8,15 @@
  *  Date#toJSON() -> String
  *
  *  Produces a string representation of the date in ISO 8601 format.
+ *  The time zone is always UTC, as denoted by the suffix "Z".
+ *
+ *  ### Example
+ *
+ *      var d = new Date(1969, 11, 31, 19);
+ *      d.getTimezoneOffset();
+ *      //-> -180 (time offest is given in minutes.)
+ *      d.toJSON();
+ *      //-> '"1969-12-31T16:00:00Z"'
 **/
 Date.prototype.toJSON = function() {
   return '"' + this.getUTCFullYear() + '-' +