title: Adding a ProjectReference to a project that is not in the same solution
body: <p>While doing some refactoring of our projects and solution files, i have separated some .sln files to contain less projects.</p>
  
  <p>Occasionally i need to reference some projects from outside the scope of the current .sln file.</p>
  
  <p>For example, my initial state was this:</p>
  
  <p>SOLUTION A</p>
  
  <ul>
  <li>PROJ A</li>
  <li>PROJ B</li>
  </ul>
  
  <p>After refactoring it would look like this:</p>
  
  <p>SOLUTION A_NEW</p>
  
  <ul>
  <li>PROJ A</li>
  </ul>
  
  <p>SOLUTION B_NEW</p>
  
  <ul>
  <li>PROJ B</li>
  </ul>
  
  <p>My question is -- Is it possible to add a <em>ProjectReference</em> node to a project that is not defined in the same VS solution? (in my case, having <strong>PROJ A</strong> have a project reference to <strong>PROJ B</strong>).</p>
  
  <p>Also, if it is possible, is that recommended?</p>
  
  <p>I know that this is not possible from the VS IDE, only by editing the .csproj file manually.</p>