             klass.prototype.PROPERTY_EFFECT_TYPES.PROPAGATE,
              {fn: createForwardHostPropEffect(prop, userForwardHostProp)});
            klass.prototype._createNotifyingProperty('_host_' + prop);
          }
        }
        upgradeTemplate(template, klass);
        // Mix any pre-bound data into __data; no need to flush this to
        // instances since they pull from the template at instance-time
        if (template.__dataProto) {
          // Note, generally `__dataProto` could be chaine