code: protected void addIndex(Content body) {
          for (String groupname : groupList) {
              List<PackageDoc> list = groupPackageMap.get(groupname);
              if (list != null && !list.isEmpty()) {
                  addIndexContents(list,
                                   groupname, configuration.getText("doclet.Member_Table_Summary",
                                                                    groupname, configuration.getText("doclet.packages")), body);
              }
          }
      }
docs: Depending upon the grouping information and their titles, add
  separate table indices for each package group.
  
  @param body the documentation tree to which the index will be added