docs: private void clear(Object caller, int version) {
          assert mutation_in_progress(caller, version);
          _buf_limit = 0;
          for (int ii=0; ii<_blocks.size(); ii++) {
              _blocks.get(ii).clearBlock();
              // _blocks.get(ii)._idx = -1; this is done in clearBlock()
          }
          bbBlock first = _blocks.get(0);
          first._idx = 0;                        // cas: 26 dec 2008
          first._offset = 0;
          first._limit = 0;
          _next_block_position = 1;
          return;
      }