code: void addParentBuffer(StreamCharBuffer parent) {
          if (!notifyParentBuffersEnabled) return;
  
          if (parentBuffers==null) {
              parentBuffers=new HashSet<SoftReference<StreamCharBufferKey>>();
          }
          parentBuffers.add(new SoftReference<StreamCharBufferKey>(parent.bufferKey));
      }
docs: /* methods for notifying child (sub) StreamCharBuffer changes to the parent StreamCharBuffer