public function removeAlias($alias) {
        $alias = $this->normalizeID($alias);

        if (!empty($this->rules[$alias]['aliasOf']) && $this->rules[$alias]['aliasOf'] !== $this->currentRuleName) {
            trigger_error("Alias '$alias' does not point to the current rule.", E_USER_NOTICE);
        }

        unset($this->rules[$alias]['aliasOf']);
        return $this;
    }