code: function appendOnFilterValue (middleware) {
    if (isErrorHandler(middleware)) {
      this.append(function (err, req, res, next) {
        if (req.__connectSequenceFilterValue) {
          middleware(err, req, res, next)
        } else {
          next()
        }
      })
    } else {
      this.append(function (req, res, next) {
        if (req.__connectSequenceFilterValue) {
          middleware(req, res, next)
        } else {
          next()
        }
      })
    }
  }
docs: Append a middleware in function of its nature and the filter value stored in req.__connectSequenceFilterValue
  @function
  @inner
  @private
  @param {Function} middleware
  @returns {undefined}