code: function (node, element) {
              var labelAsCSSName = node.label.replace(/[^0-9a-z\-_]/gi, '');
  
              var cssClass = "ppt-node__" + element;
  
              if (node.type === graph.node.NodeTypes.ROOT) {
                  cssClass = cssClass + "--root";
              }
              if (node.type === graph.node.NodeTypes.CHOOSE) {
                  cssClass = cssClass + "--choose";
              }
              if (node.type === graph.node.NodeTypes.GROUP) {
                  cssClass = cssClass + "--group";
              }
              if (node.type === graph.node.NodeTypes.VALUE) {
                  cssClass = cssClass + "--value";
              }
              if (node.value !== undefined && node.value.length > 0) {
                  cssClass = cssClass + "--value-selected";
              }
              if (node.count === 0) {
                  cssClass = cssClass + "--disabled";
              }
  
              return cssClass + " " + labelAsCSSName;
          }
docs: Generate a CSS class for the node depending on its type.
  
  @param node
  @param element
  @return {string}