title: How is dirs.proj used?
body: <p>I'm afraid I may be asking a really dumb question, but I can't seem to find anything that makes this clear.  I usually work on smaller applications but am now working on a larger one with several assemblies in a baseline framework and several assemblies for a product line domain (with more to come).  I would like to manage the build by configuring MSBuild.  I've done a lot of online research (specifically with several MSDN articles I found) and now feel knowledgeable enough to be dangerous.  </p>
  
  <p>I understand that in csharp the *.csproj file can be unloaded and modified with properties, items, and targets to control the build process.  I also understand that I can import my own targets file to help separate and organize.  In this link though (<a href="https://msdn.microsoft.com/en-us/magazine/dd483291.aspx">https://msdn.microsoft.com/en-us/magazine/dd483291.aspx</a>) a multilevel project build is organized with node-level dirs.proj files.  This is confusing to me and has raised several questions I can't seem to find an answer to:</p>
  
  <ol>
  <li>What is the difference in a *.proj and *.csproj file?</li>
  <li>Can a *.proj be setup in VS to load on Build with F6 or does using this require use of the command prompt only? (i.e. "msbuild dirs.proj /t:Build").</li>
  <li>Does dirs.proj load automatically?  If so, my study-by is not working correctly, yet it does with command prompt.</li>
  <li>Or am I overlooking something all the way around with "dirs.proj"  Maybe it's just a substitue name for one of the project *.csproj files?  If that was the case though there wouldn't have been a need for the root node's dirs.proj which from what I can tell doesn't have an actual project associated to it.  </li>
  </ol>
  
  <p>Anyways, I've seen dirs.proj mentioned in several forums regarding issues, but no where can I find how it's loaded or used in VS (outside of manual command prompt building which seems unreasonable if this is used to organize the build but the build won't really take a huge amount of time).  I'm hoping someone can help me achieve that a-ha moment with this.</p>
  
  <p>Thanks in advance.</p>