code: function getLayer(index) {
  
          // Get layer, create if necessary
          var layer = layers[index];
          if (!layer) {
  
              // Create layer based on index
              if (index === 0)
                  layer = display.getDefaultLayer();
              else if (index > 0)
                  layer = display.createLayer();
              else
                  layer = display.createBuffer();
                  
              // Add new layer
              layers[index] = layer;
  
          }
  
          return layer;
  
      }
docs: Returns the layer with the given index, creating it if necessary.
  Positive indices refer to visible layers, an index of zero refers to
  the default layer, and negative indices refer to buffers.
  
  @private
  @param {Number} index
  The index of the layer to retrieve.
  
  @return {Guacamole.Display.VisibleLayer|Guacamole.Layer}
  The layer having the given index.