code: function init (model) {
      if (model.__ttl) return;
  
      var distinct_ = model.distinct;
      model.distinct = function distinct (field, cond, cb) {
        applyTTL(cond);
        return distinct_.call(model, field, cond, cb);
      }
  
      'findOne find count'.split(' ').forEach(function (method) {
        var fn = model[method];
  
        model[method] = function (cond, fields, opts, cb) {
          if (!cond) {
            cond = {};
          } else if ('function' == typeof cond) {
            cb = cond;
            cond = {};
          }
  
          applyTTL(cond);
          return fn.call(model, cond, fields, opts, cb);
        }
      });
  
      'where $where'.split(' ').forEach(function (method) {
        var fn = model[method];
        model[method] = function () {
          var query = fn.apply(this, arguments)
            , cond = {};
          applyTTL(cond);
          return query.find(cond);
        }
      });
  
      if (reap) {
        model.startTTLReaper();
      }
    }
docs: init
  
  Hook into all model queries to include the TTL
  filter and kick off the expired doc reaper if
  enabled.
  @private