code: function( elem, dd ){
                  var offset = (elem && elem.ownerDocument) 
                      ? $( elem )[ dd.relative ? "position" : "offset" ]() || { top:0, left:0 }
                      : { top: 0, left: 0 };
                  return {
                      drag: elem,
                      callback: new drag.callback(),
                      droppable: [],
                      offset: offset
                  };
              }
docs: returns an interaction object