title: EventCreate.exe creates a "CustomSource" value, what does it mean?
body: <p>The command-line <code>EventCreate.exe</code> tool registers a user-defined event source in the Registry for the Windows Event Log Viewer to use, like this:</p>
  
  <pre><code>eventcreate /t INFORMATION /ID 100 /L "Application" /SO [SourceName] /D "Description"
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/E7xuw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/E7xuw.png" alt="image"></a></p>
  
  <p>I wrote an app that has its own Event Log resource strings and is registered as an event source, <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa363661.aspx" rel="nofollow noreferrer">per MSDN</a>, but it doesn't use the <code>CustomSource</code> value and works fine.</p>
  
  <p>I can't find any documentation on MSDN, or elsewhere online, on what <code>CustomSource</code> is meant for exactly.  None of the registered sources on my machines use it.</p>
  
  <p>Does anyone know what <code>CustomSource</code> is meant for, and how it works?  Is it just something internal to <code>EventCreate.exe</code>, or does the Windows Event Log actually use it for something?</p>