docs: function watch(obj, _keyPath, m) {
        // can't watch length on Array - it is special...
        if (_keyPath === 'length' && typeOf(obj) === 'array') { return; }
  
        if (!isPath(_keyPath)) {
          watchKey(obj, _keyPath, m);
        } else {
          watchPath(obj, _keyPath, m);
        }
      }