// Before:
inboxRecyclerView.expandItem(adapterId = 42)
// After:
val itemExpander = InboxItemExpander { expandingItemKey, viewHolders ->
  viewHolders.firstOrNull { holder ->
    // Identify the expanding item's ViewHolder here. Otherwise return
    // null to expand the item from the top of the list.
    holder.{some identifier} == expandingItemKey 
  }
}
inboxRecyclerView.itemExpander = itemExpander
itemExpander.expandItem(item = ExpandableScreenKey(...))