title: Targeting both .NET 3.5 and Silverlight
body: <p>Let's imagine I already have a project building .NET 3.5 assembly. Now I want to build this assembly for Silverlight, and moreover, maintain its Silverlight version with minimal efforts further.</p>
  
  <p><strong>What is not acceptable:</strong></p>
  
  <ul>
  <li>Creating separate project for Silverlight build</li>
  </ul>
  
  <p><strong>What is acceptable:</strong></p>
  
  <ul>
  <li>Adding custom  directives allowing me to target either Silverlight or .NET dependently on e.g. MSBuild properties.</li>
  <li>Adding special build configurations for Silverlight</li>
  <li>Adding #ifdef Silverlight / #endif sections to the source code.</li>
  <li>Generally any other modification of .csproj / .cs.</li>
  </ul>
  
  <p>So basically, I'd like to maintain a single project, but target two frameworks. I don't want to maintain two separate projects, because this may lead to mistakes like forgetting to include a new file. If there are many project and big team, this is really important to exclude such mistakes.</p>
  
  <p>If this is completely impossible, any solution providing similar benefits is acceptable.</p>