title: Attach base class to Unity3D scene or project
body: <p>Per scene in Unity3D, I always require some base class implementing interfaces and functionality such as delegating events for changing scenes via <code>Application.LoadLevel()</code>.</p>
  
  <p>Typically I've attached these scripts to the Camera; however, I'm not sure this is a best practice especially when multiple cameras are present.</p>
  
  <p>How is a base class for a scene specified?</p>
  
  <p>When the scene is selected from the project no components may be added nor any option available in the inspector.</p>
  
  <p><img src="https://i.stack.imgur.com/BcXBE.png" alt="unity-project"></p>
  
  <p><img src="https://i.stack.imgur.com/2iQqi.png" alt="unity-inspector"></p>
  
  <p>How would I subtype or attach a base class directly to the scene?</p>
  
  <p>Likewise for an entire Unity3D project, is there any way to base class or subtype to enable code for a Unity application independent of scenes?</p>