docs: function (appender, opts) {
              var args = argsToArray(arguments);
              if (isString(appender)) {
                  this.addAppender(Appender.createAppender(appender, opts));
              } else {
                  if (!isUndefinedOrNull(appender)) {
  
                      var name = appender.name;
                      if (!(name in this.__appenders)) {
                          this.__appenders[name] = appender;
                          if (!appender.level) {
                              appender.level = this.level;
                          }
                          this._tree.addAppender(appender);
                      }
                  }
              }
              return this;
          }