title: What's the meaning of square brackets [ ] in WiX?
body: <p>I'm creating an installer for an IIS website using the WiX toolset and I use <a href="http://blog.bartdemeyer.be/2013/10/create-an-installer-for-website-with-wix-part-3/" rel="nofollow noreferrer">this</a> manual. I've came across the following syntax:</p>
  
  <pre><code>&lt;iis:WebSite Id=&quot;DemoWebsiteWebsite&quot; Description='Demo Website' Directory='INSTALLFOLDER' AutoStart='yes' StartOnInstall='yes'&gt;
    &lt;iis:WebAddress Id=&quot;AllUnassigned&quot; Port=&quot;80&quot; /&gt;
    &lt;iis:WebApplication Id=&quot;DemoWebsiteApplication&quot; Name=&quot;[DemoWebsiteWebsite][WEBSITE_ID]&quot; WebAppPool=&quot;DemoWebsiteAppPool&quot;&gt;&lt;/iis:WebApplication&gt;
  &lt;/iis:WebSite&gt;
  </code></pre>
  <p>I'm confused by the <code>[]</code> syntax and the way website id is used here. I need to use some custom values entered by user for that. So I have the following questions:</p>
  <ol>
  <li>What does the <code>[]</code> syntax mean in WiX? How is it related to the <code>$()</code> syntax that is used to access the defined value?</li>
  <li>Is there any additional meaning for two <code>[]</code> following each other like here <code>[DemoWebsiteWebsite][WEBSITE_ID]</code>?</li>
  <li>Why the WebSite Id is used in <code>[DemoWebsiteWebsite]</code> expression? Is that just a coincidence or naming convention?</li>
  <li>What are the allowed values to be used inside <code>[]</code>? Is there any kind of list for them?</li>
  <li>Where can I find additional info about this syntax and cases it is used for?</li>
  </ol>