bool mergeAllDescendantsIntoThisNode

Whether all this node and all of its descendants should be treated as one logical entity.

Source 

bool get mergeAllDescendantsIntoThisNode => _mergeAllDescendantsIntoThisNode;
void mergeAllDescendantsIntoThisNode=(bool value)

Source 

set mergeAllDescendantsIntoThisNode(bool value) {
  assert(value != null);
  if (_mergeAllDescendantsIntoThisNode == value)
    return;
  _mergeAllDescendantsIntoThisNode = value;
  _markDirty();
}