code: protected void addClassList(Content contentTree) throws IOException {
          String[] classTableHeader = new String[] {
              configuration.getText("doclet.0_and_1",
                      configuration.getText("doclet.Class"),
                      configuration.getText("doclet.Description"))
          };
          Iterator<String> itp = usingPackageToUsedClasses.keySet().iterator();
          while (itp.hasNext()) {
              String packageName = itp.next();
              PackageDoc usingPackage = configuration.root.packageNamed(packageName);
              HtmlTree li = new HtmlTree(HtmlTag.LI);
              li.addStyle(HtmlStyle.blockList);
              if (usingPackage != null) {
                  li.addContent(getMarkerAnchor(usingPackage.name()));
              }
              String tableSummary = configuration.getText("doclet.Use_Table_Summary",
                      configuration.getText("doclet.classes"));
              Content table = HtmlTree.TABLE(HtmlStyle.useSummary, 0, 3, 0, tableSummary,
                      getTableCaption(configuration.getResource(
                      "doclet.ClassUse_Classes.in.0.used.by.1",
                      getPackageLink(pkgdoc, Util.getPackageName(pkgdoc)),
                      getPackageLink(usingPackage, Util.getPackageName(usingPackage)))));
              table.addContent(getSummaryTableHeader(classTableHeader, "col"));
              Content tbody = new HtmlTree(HtmlTag.TBODY);
              Iterator<ClassDoc> itc =
                      usingPackageToUsedClasses.get(packageName).iterator();
              for (int i = 0; itc.hasNext(); i++) {
                  HtmlTree tr = new HtmlTree(HtmlTag.TR);
                  if (i % 2 == 0) {
                      tr.addStyle(HtmlStyle.altColor);
                  } else {
                      tr.addStyle(HtmlStyle.rowColor);
                  }
                  addClassRow(itc.next(), packageName, tr);
                  tbody.addContent(tr);
              }
              table.addContent(tbody);
              li.addContent(table);
              contentTree.addContent(li);
          }
      }
docs: Add the list of classes that use the given package.
  
  @param contentTree the content tree to which the class list will be added