code: function( arg ){
  
              var i = 0
                  ,len = arg && arg.length || 0
                  ,thing = Physics.util.isArray( arg ) ? arg[ 0 ] : arg
                  ;
  
              if ( !thing ){
                  return this;
              }
  
              // we'll either cycle through an array
              // or just run this on the arg itself
              do {
                  switch (thing.type){
  
                      case 'behavior':
                          this.addBehavior(thing);
                      break; // end behavior
  
                      case 'integrator':
                          this.integrator(thing);
                      break; // end integrator
  
                      case 'renderer':
                          this.renderer(thing);
                      break; // end renderer
  
                      case 'body':
                          this.addBody(thing);
                      break; // end body
  
                      default:
                          throw 'Error: failed to add item of unknown type "'+ thing.type +'" to world';
                      // end default
                  }
  
              } while ( ++i < len && (thing = arg[ i ]) );
  
              return this;
          }
docs: chainable
  Physics.world#add( things ) -> this
  - things (Object|Array): The thing, or array of things (body, behavior, integrator, or renderer) to add.
  
  Multipurpose add method. Add one or many bodies, behaviors, integrators, renderers...