code: function (array, items, fnEqual) {
          
          if (   !(array instanceof Array)
              || !(items instanceof Array) )
              throw "IllegalArgumentException: expected two Array arguments.";
          
          var isMod = false;
          for (var i = 0, len = items.length; i < len; i++) {
              if (Arrays.addIfMissing(items[i], array, fnEqual))
                  isMod = true;
          }
          
          return isMod;
      }
docs: This function adds each item from <code>items</code>
  into <code>array</code>, but only if the item isn't
  already in the array.
  
  Note: this function may modify <code>array</code>.
  
  @param array {Array}
  @param items {Array}
  @param fnEqual {Function} Optional.
  {Boolean} Whether <code>array</code> was modified.