code: function (node) {
              var size = provider.node.getSize(node);
              return [
                  {
                      "d": "M 0, 0 m -" + size + ", 0 a " + size + "," + size + " 0 1,0 " + 2 * size + ",0 a " + size + "," + size + " 0 1,0 -" + 2 * size + ",0",
                      "fill": "transparent",
                      "stroke": provider.node.getColor(node),
                      "stroke-width": "2px"
                  }
              ];
          }
docs: Function returning a array of path objects to display in the node.
  
  @param node
  @returns {*[]}