code: private AttributeUpdate generateBackpointerUpdate(long fromOffset, long toOffset) {
          return new AttributeUpdate(getBackpointerAttributeKey(fromOffset), AttributeUpdateType.Replace, toOffset);
      }
docs: Generates an AttributeUpdate that creates a new or updates an existing Backpointer.
  
  @param fromOffset The offset at which the Backpointer originates.
  @param toOffset   The offset at which the Backpointer ends.