title: What is maven.multiModuleProjectDirectory used for?
body: <p>I've seen a lot of chatter regarding setting an env parameter <code>maven.multiModuleProjectDirectory</code>, both on SO and on Maven mailing lists, but I am having trouble understanding exactly what this setting does/is used for.</p>
  
  <p>I've searched google, maven sites, docs, etc, but can't seem to find a reference that actually explains what this parameter is for, or how to leverage it.</p>
  
  <p>Can anyone either explain it's purpose and/or point me to the documentation for it?  In which version of maven was it introduced?</p>