code: func (bp *BasePermissions) Set(ty PermFlag, value bool) error {
  	if ty == 0 {
  		return ErrInvalidPermission(ty)
  	}
  	bp.SetBit |= ty
  	if value {
  		bp.Perms |= ty
  	} else {
  		bp.Perms &= ^ty
  	}
  	return nil
  }
docs: // Set a permission bit. Will set the permission's set bit to true.