mer.Path
     * @param {string} path Path string
     * @return {string} Root property name
     */
    root: function(path) {
      let dotIndex = path.indexOf('.');
      if (dotIndex === -1) {
        return path;
      }
      return path.slice(0, dotIndex);
    },

    /**
     * Given `base` is `foo.bar`, `foo` is an ancestor, `foo.bar` is not
     * Returns true if the given path is an ancestor of the base path.
     *
     * Example:
     *
     * ```
     * Polymer.Path.isAncestor('foo.bar', 'foo')