wix - 属性名称前的 '&' 和 '!' 是什么意思？

Question

我正在阅读其他人编写的 WIX 脚本。有一些代码真的让我感到困惑。

<Custom Action='UnLoadSchedulerPerfCounters' After='InstallInitialize'>
    <![CDATA[(Installed) AND (!Scheduler = 3)]]>
</Custom>
<Custom Action='RollbackSchedulerPerfCounters' After='WriteRegistryValues'>
        <![CDATA[(&Scheduler = 3)]]>
</Custom>

那么， !Scheduler 和有什么区别？和 &Scheduler ?
当属性以 & 为前缀时有什么特殊含义吗？或 ! ?

Answer 1

来自 http://www.tramontana.co.hu/wix/lesson5.php#5.3 :

Prepending some special characters to the names will give them extra meaning:

%     environment variable (name is case insensitive)
$     action state of component
?     installed state of component
&     action state of feature
!     installed state of feature

The last four can return the following integer values:

-1   no action to be taken
1    advertised (only for components)
2    not present
3    on the local computer
4    run from the source