code: func (y EngineYard) Default() Engine {
  	d, ok := y[DefaultEngine]
  	if !ok {
  		// This is a developer error!
  		panic("Default template engine does not exist")
  	}
  	return d
  }
docs: // Default returns the default template engine.
  //
  // The default is specified by DefaultEngine.
  //
  // If the default template engine cannot be found, this panics.