Function updateFragment

packages/react-reconciler/src/ReactFiberBeginWork.js:1333–1344

(
  current: Fiber | null,
  workInProgress: Fiber,
  renderLanes: Lanes,
)

}

function updateFragment(
  current: Fiber | null,
  workInProgress: Fiber,
  renderLanes: Lanes,
) {
  const nextChildren = workInProgress.pendingProps;
  if (enableFragmentRefs) {
    markRef(current, workInProgress);
  }
  reconcileChildren(current, workInProgress, nextChildren, renderLanes);
  return workInProgress.child;
}

function updateMode(
  current: Fiber | null,