sclass HTMLFramer1 {
  S title;
  bool titleIsHTML;
  new L<NavItem> navItems;
  new L<O> contents; // items will be evaluated to strings upon rendering
  new LinkedHashSet<S> headElements; // automatically avoid duplication
  bool navBeforeTitle;
  new L<Runnable> willRender;

  srecord NavItem(S link, S html) {
    bool targetBlank;
  }
  
  public S get() { ret render(); }
  
  swappable S render() {
    callFAll(willRender);
    ret hhtml(hhead(htitle(titleIsHTML ? hTitleClean(title) : title)
      + lines(headElements))
      + hbody(
        (navBeforeTitle ? renderNav() + renderTitle()
          : renderTitle() + renderNav())
        + nemptyLines(contents)));
  }
  
  swappable S renderTitle() {
    ret h1(encodedTitle());
  }
  
  S encodedTitle() {
    //printVars_str encodedTitle(+title, +titleIsHTML);
    ret titleIsHTML ? title : htmlEncode2(title);
  }
  
  swappable S renderNav() {
    if (empty(navItems)) ret "";
    ret div_vbar(map renderNavItem(navItems), style := "margin-bottom: 0.5em");
  }
  
  S renderNavItem(NavItem ni) {
    ret ahref_possiblyTargetBlank(ni.link, ni.html, ni.targetBlank);
  }
  
  void addNavItem(S html) {
    navItems.add(new NavItem(null, html));
  }
  
  void addNavItems(Iterable<S> htmls) {
    forEach addNavItem(htmls);
  }
  
  void addNavItem(S link, S html, O... _) {
    navItems.add(setAll(new NavItem(link, html), filterParams(_, 'targetBlank)));
  }
  
  void addInHead aka addInHEAD(O html) {
    headElements.add(str(html));
  }
  
  // legacy signature for binary compatibility
  void add(S html) { add((O) html); }
  
  // convenience signature for lambdas
  void add(IF0<O> html) { add(lambdaToToString(html)); }
  
  // add contents: TODO move things to head automatically
  void add(O html) {
    if (notNullOrEmptyString(html))
      contents.add(html);
  }
  
  void addAll(Cl<S> l) { forEach add(l); }
  
  void clearNavItems {
    navItems.clear();
  }
  
  selfType setTitle(S title) {
    this.title = title;
    this;
  }
  
  S htmlTitle(S title) {
    this.title = title;
    titleIsHTML = true;
    ret title;
  }
  
  Cl<S> headElements() { ret headElements; }
}