void* value = aFrame->GetProperty(nsLayoutAtoms::IBSplitSpecialSibling);
void* value = aFrameManager->GetFrameProperty(aFrame, nsLayoutAtoms::IBSplitSpecialSibling, 0);
GetSpecialSibling(nsFrameManager* aFrameManager, nsIFrame* aFrame, nsIFrame** aResult){  // We only store the "special sibling" annotation with the first  // frame in the flow. Walk back to find that frame now.  aFrame = aFrame->GetFirstInFlow();  void* value = aFrame->GetProperty(nsLayoutAtoms::IBSplitSpecialSibling);  *aResult = NS_STATIC_CAST(nsIFrame*, value);}