docs: function (fn) {
          if(validateFn(fn)){
              this.list.push(fn);
          }else if(Object.prototype.toString.call(fn) === "[object Array]"){
              for(var i = 0, len = fn.length; i < len; i++){
                   arguments.callee.call(this, fn[i]);   
              }
          }
  
          return this;
      }