1. override
void attach(SemanticsOwner owner)

Mark this node as attached to the given owner.

Typically called only from the parent's attach method, and by the owner to mark the root of a tree as attached.

Subclasses with children should attach all their children to the same owner whenever this method is called.

Source 

@override
void attach(SemanticsOwner owner) {
  super.attach(owner);
  assert(!owner._nodes.containsKey(id));
  owner._nodes[id] = this;
  owner._detachedNodes.remove(this);
  if (_dirty) {
    _dirty = false;
    _markDirty();
  }
  if (parent != null)
    _inheritedMergeAllDescendantsIntoThisNode = parent._shouldMergeAllDescendantsIntoThisNode;
  if (_children != null) {
    for (SemanticsNode child in _children)
      child.attach(owner);
  }
}