docs: function writableBy(file, user) {
    function _writableBy(f, userData) {
      if (!exists(f)) {
        return _writableBy(path.dirname(f), userData);
      } else {
        return _accesibleByUser(userData, f, fs.W_OK);
      }
    }
    const uData = findUser(user);
    // root can always write
    if (uData.id === 0) {
      return true;
    } else if (uData.id === process.getuid()) {
      return writable(file);
    } else {
      return _writableBy(file, uData);
    }
  }