docs: private final Object[] help_copy( Object[] helper ) {
      // Read the top-level KVS only once.  We'll try to help this copy along,
      // even if it gets promoted out from under us (i.e., the copy completes
      // and another KVS becomes the top-level copy).
      Object[] topkvs = _kvs;
      CHM topchm = chm(topkvs);
      if( topchm._newkvs == null ) return helper; // No copy in-progress
      topchm.help_copy_impl(this,topkvs,false);
      return helper;
    }