anchor.diff:  
   -type req_id() :: non_neg_integer().
   -type from() :: {atom(), req_id(), pid()}.
  +-type pvc() :: all | pos_integer().
  +-type request() :: tuple().
   -type vnode_selector() :: all | allup.
  --type primary_vnode_coverage() :: all | pos_integer().
  -
   -record(state, {coverage_vnodes :: [{non_neg_integer(), node()}],
                   mod :: atom(),
                   mod_state :: mod_state(),
                   n_val :: pos_integer(),
                   node_check_service :: module(),
  -                vnode_selector :: all | allup | {colocated, atom()},
  -                pvc :: all | pos_integer(), % primary vnode coverage
  -                request :: tuple(),
  +                vnode_selector :: vnode_selector(),
  +                pvc :: pvc(), % primary vnode coverage
  +                request :: request(),
                   req_id :: req_id(),
                   required_responses :: pos_integer(),
                   response_count=0 :: non_neg_integer(),
  
positive.code:                 plan_fun :: function(),
                  process_fun :: function()
                 }).
  
  %% ===================================================================
  %% Public API
  
negative.code: %% ====================================================================
  %% gen_fsm callbacks
  %% ====================================================================
  %% @private
  init([Mod,
        From={_, ReqId, _},
  