title: What are merge modules and how are they used?
body: <p>What are merge modules and how are they used? I heard that they are .msm files, but I've never seen that before (I've only seen .msi).</p>
  
  <p>Are they used when you create msi files?
  Are they distributed with commercial software (presumably together with msi files?)</p>
  
  <p>What is the point of them? Are they to hide the implementation of the installer for common third party or Microsoft components that need to be installed together with developed software (and therefore distributed together)?</p>
  
  <p>Thanks!</p>