docs: function (chrs, buffer, pos, strict, opts) {
                          if (opts.isInYearRange(chrs, opts.yearrange.minyear, opts.yearrange.maxyear)) {
                              var dayMonthValue = buffer.join('').substr(0, 6);
                              if (dayMonthValue != opts.leapday)
                                  return true;
                              else {
                                  var year = parseInt(chrs, 10);//detect leap year
                                  if (year % 4 === 0)
                                      if (year % 100 === 0)
                                          if (year % 400 === 0)
                                              return true;
                                          else return false;
                                      else return true;
                                  else return false;
                              }
                          } else return false;
                      }