code: function( event, dd, ia ){
                  var obj = ia.callback;
                  // elements
                  obj.drag = ia.drag;
                  obj.proxy = ia.proxy || ia.drag;
                  // starting mouse position
                  obj.startX = dd.pageX;
                  obj.startY = dd.pageY;
                  // current distance dragged
                  obj.deltaX = event.pageX - dd.pageX;
                  obj.deltaY = event.pageY - dd.pageY;
                  // original element position
                  obj.originalX = ia.offset.left;
                  obj.originalY = ia.offset.top;
                  // adjusted element position
                  obj.offsetX = obj.originalX + obj.deltaX;
                  obj.offsetY = obj.originalY + obj.deltaY;
                  // assign the drop targets information
                  obj.drop = drag.flatten( ( ia.drop || [] ).slice() );
                  obj.available = drag.flatten( ( ia.droppable || [] ).slice() );
                  return obj;
              }
docs: extend the callback object with drag/drop properties...