return (
      rect.top >= 0 &&
      rect.left >= 0 &&
      rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
      rect.right <= (window.innerWidth || document.documentElement.clientWidth)
    );
  };

  const ForceResizeKludge = 0 ? function(){} : (function(){
    /* Workaround for Safari mayhem regarding use of vh CSS units....
       We tried to use vh units to set the content area size for the
       chat layout, but Safari chokes on that, so we calculate that
       height here: 85% when in "normal" mode and 95% in chat-only
       mode. Larger than ~95% is too big for Firefox on Android,
       causing the input area to move off-screen. */
    const contentArea = E1('div.content'),
          bcl = document.body.classList;
    const resized = function(){
      const wh = window.innerHeight,
            mult = bcl.contains('chat-only-mode') ? 0.95 : 0.85;
      contentArea.style.maxHeight = (wh * mult)+"px";
      console.debug("resized.",wh, mult, window.getComputedStyle(contentArea).maxHeight);
    };
    var doit;
    window.addEventListener('resize',function(ev){
      clearTimeout(doit);
      doit = setTimeout(resized, 100);
    }, false);
    resized();
    return resized;
  })();

  const Chat = (function(){
    const cs = {
      e:{/*map of certain DOM elements.*/
        messageInjectPoint: E1('#message-inject-point'),
        pageTitle: E1('head title'),
        loadOlderToolbar: undefined /* the load-posts toolbar (dynamically created) */,
        inputWrapper: E1("#chat-input-area"),

           to avoid various race conditions in the UI and long-running
           network requests. */
      ],
      /* Injects element e as a new row in the chat, at the top of the
         list if atEnd is falsy, else at the end of the list, before
         the load-history widget. */
      injectMessageElem: function f(e, atEnd){
        const mip = atEnd ? this.e.loadOlderToolbar : this.e.messageInjectPoint;
        /* Reminder: this placement is kinda odd because of the
           flex-direction:column-reverse in this.e.messagesWrapper,
           which reverses our directions. */
        if(atEnd){
          mip.parentNode.insertBefore(e, mip);
        }else{
          const fe = mip.nextElementSibling;
          if(fe) mip.parentNode.insertBefore(e, fe);
          else D.append(mip.parentNode, e);


        }
        if(!atEnd && !this.isMassLoading
           && e.dataset.xfrom!==Chat.me && !isInViewport(e)){
          /* If a new non-history message arrives while the user is
             scrolled elsewhere, do not scroll to the latest
             message, but gently alert the user that a new message
             has arrived. */
          F.toast.message("New message has arrived.");
        }else if(e.dataset.xfrom===Chat.me){
          e.scrollIntoView();
        }
      },
      /** Returns true if chat-only mode is enabled. */
      isChatOnlyMode: ()=>document.body.classList.contains('chat-only-mode'),
      /**
         Enters (if passed a truthy value or no arguments) or leaves
         "chat-only" mode. That mode hides the page's header and

          document.body.scroll(0,document.body.height);
        }else{
          D.removeClass(f.elemsToToggle, 'hidden');
          D.removeClass(document.body, 'chat-only-mode');
        }
        const msg = document.querySelector('.message-widget');
        if(msg) setTimeout(()=>msg.scrollIntoView(),0);
        ForceResizeKludge();
        return this;
      },
      toggleChatOnlyMode: function(){
        return this.chatOnlyMode(!this.isChatOnlyMode());
      },
      settings:{
        get: (k,dflt)=>F.storage.get(k,dflt),