code: func (bp BasePermissions) Get(ty PermFlag) (bool, error) {
  	if ty == 0 {
  		return false, ErrInvalidPermission(ty)
  	}
  	if !bp.IsSet(ty) {
  		return false, ErrValueNotSet(ty)
  	}
  	return bp.Perms&ty == ty, nil
  }
docs: // Gets the permission value.
  // ErrValueNotSet is returned if the permission's set bits are not all on,
  // and should be caught by caller so the global permission can be fetched