docs: function assignFiberPropertiesInDEV(target, source) {
    if (target === null) {
      // This Fiber's initial properties will always be overwritten.
      // We only use a Fiber to ensure the same hidden class so DEV isn't slow.
      target = createFiber(IndeterminateComponent, null, null, NoContext);
    }
  
    // This is intentionally written as a list of all properties.
    // We tried to use Object.assign() instead but this is called in
    // the hottest path, and Object.assign() was too slow:
    // https://github.com/facebook/react/issues/12502
    // This code is DEV-only so size is not a concern.
  
    target.tag = source.tag;
    target.key = source.key;
    target.elementType = source.elementType;
    target.type = source.type;
    target.stateNode = source.stateNode;
    target.return = source.return;
    target.child = source.child;
    target.sibling = source.sibling;
    target.index = source.index;
    target.ref = source.ref;
    target.pendingProps = source.pendingProps;
    target.memoizedProps = source.memoizedProps;
    target.updateQueue = source.updateQueue;
    target.memoizedState = source.memoizedState;
    target.contextDependencies = source.contextDependencies;
    target.mode = source.mode;
    target.effectTag = source.effectTag;
    target.nextEffect = source.nextEffect;
    target.firstEffect = source.firstEffect;
    target.lastEffect = source.lastEffect;
    target.expirationTime = source.expirationTime;
    target.childExpirationTime = source.childExpirationTime;
    target.alternate = source.alternate;
    if (enableProfilerTimer) {
      target.actualDuration = source.actualDuration;
      target.actualStartTime = source.actualStartTime;
      target.selfBaseDuration = source.selfBaseDuration;
      target.treeBaseDuration = source.treeBaseDuration;
    }
    target._debugID = source._debugID;
    target._debugSource = source._debugSource;
    target._debugOwner = source._debugOwner;
    target._debugIsCurrentlyTiming = source._debugIsCurrentlyTiming;
    target._debugHookTypes = source._debugHookTypes;
    return target;
  }