docs: private int insertInCurrOnly(Object caller, int version, bbBlock curr, int pos, int len)
      {
          assert mutation_in_progress(caller, version);
          // the space we need is available right in the block
          assert curr.unusedBlockCapacity() >= len;
          System.arraycopy(curr._buffer, curr.blockOffsetFromAbsolute(pos)
                           ,curr._buffer, curr.blockOffsetFromAbsolute(pos) + len, curr.bytesAvailableToRead(pos));
          curr._limit += len;
          this.adjustOffsets(curr._idx, len, 0);
          notifyInsert(pos, len);
          return len;
      }