docs: function( topic, fn, scope ){
  
              // check if we're subscribing to multiple topics
              // with an object
              if ( Physics.util.isObject( topic ) ){
  
                  for ( var t in topic ){
  
                      this.one( t, topic[ t ], fn, scope );
                  }
  
                  return this;
              }
  
              // set the _one_ flag
              fn._one_ = true;
              this.on( topic, fn, scope );
  
              return this;
          }