code: protected void setTopFile(DocletEnvironment docEnv) {
          if (!checkForDeprecation(docEnv)) {
              return;
          }
          if (createoverview) {
              topFile = DocPaths.overviewSummary(frames);
          } else {
              if (showModules) {
                  topFile = DocPath.empty.resolve(DocPaths.moduleSummary(modules.first()));
              } else if (packages.size() == 1 && packages.first().isUnnamed()) {
                  List<TypeElement> classes = new ArrayList<>(getIncludedTypeElements());
                  if (!classes.isEmpty()) {
                      TypeElement te = getValidClass(classes);
                      topFile = DocPath.forClass(utils, te);
                  }
              } else if (!packages.isEmpty()) {
                  topFile = DocPath.forPackage(packages.first()).resolve(DocPaths.PACKAGE_SUMMARY);
              }
          }
      }
docs: Decide the page which will appear first in the right-hand frame. It will
  be "overview-summary.html" if "-overview" option is used or no
  "-overview" but the number of packages is more than one. It will be
  "package-summary.html" of the respective package if there is only one
  package to document. It will be a class page(first in the sorted order),
  if only classes are provided on the command line.
  
  @param docEnv the doclet environment