function unassign($Role, $UserID = null)
	{
	    if ($UserID === null)
	        throw new \RbacUserNotProvidedException ("\$UserID is a required argument.");

	    if (is_numeric($Role))
	    {
	        $RoleID = $Role;

	    } else {

	        if (substr($Role, 0, 1) == "/")
	            $RoleID = Jf::$Rbac->Roles->pathId($Role);
	        else
	            $RoleID = Jf::$Rbac->Roles->titleId($Role);
	    }

	    return Jf::sql("DELETE FROM {$this->tablePrefix()}userroles WHERE UserID=? AND RoleID=?", $UserID, $RoleID) >= 1;
	}