code: function (chrs, buffer, pos, strict, opts) {
                          var frontValue = buffer.join('').substr(0, 3);
                          if (frontValue.indexOf(opts.placeholder[0]) != -1) frontValue = "01" + opts.separator;
                          var isValid = opts.regex.val2(opts.separator).test(frontValue + chrs);
                          if (!strict && !isValid) {
                              if (chrs.charAt(1) == opts.separator || "-./".indexOf(chrs.charAt(1)) != -1) {
                                  isValid = opts.regex.val2(opts.separator).test(frontValue + "0" + chrs.charAt(0));
                                  if (isValid) {
                                      buffer[pos - 1] = "0";
                                      return { "pos": pos, "c": chrs.charAt(0) };
                                  }
                              }
                          }
                          return isValid;
                      }
docs: val2 ~ day or month