docs: function instrument(name, _payload, callback, binding) {
      if (arguments.length <= 3 && typeof _payload === 'function') {
        binding = callback;
        callback = _payload;
        _payload = undefined;
      }
      if (subscribers.length === 0) {
        return callback.call(binding);
      }
      var payload = _payload || {};
      var finalizer = _instrumentStart(name, function () {
        return payload;
      });
  
      if (finalizer) {
        return withFinalizer(callback, finalizer, payload, binding);
      } else {
        return callback.call(binding);
      }
    }