code: function( renderer ){
  
              if ( renderer === undefined ){
                  return this._renderer;
              }
  
              // do nothing if renderer already added
              if ( this._renderer === renderer ){
                  return this;
              }
  
              if ( this._renderer ){
  
                  this._renderer.setWorld( null );
  
                  this.emit( 'remove:renderer', {
                      renderer: this._renderer
                  });
              }
  
              if ( renderer ){
                  this._renderer = renderer;
                  this._renderer.setWorld( this );
  
                  this.emit( 'add:renderer', {
                      renderer: this._renderer
                  });
              }
  
              return this;
          }
docs: chainable
  Physics.world#renderer( [renderer] ) -> Renderer|this
  - renderer (Renderer): The renderer to set on the world
  + (Renderer): The currently set renderer if `renderer` not specified
  + (this): for chaining if `renderer` specified
  
  Get or Set the renderer