title: How do I create a conditional property in WiX? (Almost like an If-Then)
body: <p>I have a WiX project that installs a few EXE files. One is the 'Main' executable and the others are supporting programs to help diagnose problems.</p>
  
  <p>The main executable is optional, and the support programs will run on their own. Often, the end user will install a third-party program instead of my main executable.</p>
  
  <p>At the end of the WiX installer, I want to have a 'launch program' checkbox that will run the program as soon as the installer closes.</p>
  
  <p>I can hide the checkbox based on the INSTALLLEVEL property, but that only changes depending on if the user selected a 'Typical' or 'Complete' install. I would like to hide it based on if the main executable feature is installed or not.</p>
  
  <p>Something like this would be ideal:</p>
  
  <pre><code>&lt;Feature Id='MainProgram' Title='MainExe'
           Description='This application stores and displays information from our hardware.'
           ConfigurableDirectory='INSTALLDIR' Level='4'
           AllowAdvertise='no'&gt;
      &lt;ComponentRef Id='MainExecutable' /&gt;
      &lt;ComponentRef Id='SQLLibrary' /&gt;
      &lt;ComponentRef Id='ProgramIcon' /&gt;
      &lt;ComponentRef Id='RemovePluginsFolder'/&gt;
      &lt;Property Id='ShowFinalCheckbox'&gt;1&lt;/Property&gt; #&lt;--This won't work, but I'd like it to.
  &lt;/Feature&gt;
  </code></pre>