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

  (function(){
    let dbg = document.querySelector('#debugMsg');
    if(dbg){
      /* This can inadvertently influence our flexbox layouts, so move
         it out of the way. */
      D.append(document.body,dbg);
    }
  })();
  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. */

      },
      disableDuringAjax: [
        /* List of DOM elements disable while ajax traffic is in
           transit. Must be populated before ajax starts. We do this
           to avoid various race conditions in the UI and long-running
           network requests. */
      ],
      /** Either scrolls .message-widget element eMsg into view
          immediately or, if it represents an inlined image, delays
          the scroll until the image is loaded, at which point it will
          scroll to either the newest message, if one is set or to
          eMsg (the liklihood is good, at least on initial page load,
          that the the image won't be loaded until other messages have
          been injected). */
      scheduleScrollOfMsg: function(eMsg){
        if(1===+eMsg.dataset.hasImage){
          console.debug("Delaying scroll for IMG.");
          eMsg.querySelector('img').addEventListener(
            'load', ()=>(this.e.newestMessage || eMsg).scrollIntoView()
          );
        }else{
          eMsg.scrollIntoView();
        }
        return this;
      },
      /* 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,
              holder = this.e.messagesWrapper;
              holder = this.e.messagesWrapper,
              prevMessage = this.e.newestMessage;
        if(atEnd){
          const fe = mip.nextElementSibling;
          if(fe) mip.parentNode.insertBefore(e, fe);
          else D.append(mip.parentNode, e);
        }else{
          D.append(holder,e);
          Chat.newestMessageElem = e;
          this.e.newestMessage = e;
        }
        if(!atEnd && !this.isMassLoading
           && e.dataset.xfrom!==Chat.me && !isInViewport(e)){
           && e.dataset.xfrom!==this.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();
        }else if(!this.isMassLoading && e.dataset.xfrom===Chat.me){
          this.scheduleScrollOfMsg(e);
        }else if(!this.isMassLoading){
          /* When a message from someone else arrives, we have to
             figure out whether or not to scroll it into view. Ideally
             we'd just stuff it in the UI and let the flexbox layout
             DTRT, but Safari has expressed, in no uncertain terms,
             some disappointment with that approach, so we'll
             heuristicize it: if the previous last message is in view,
             assume the user is at or near the input element and
             scroll this one into view. If that message is NOT in
             view, assume the user is up reading history somewhere and
             do NOT scroll because doing so would interrupt
             them. There are middle grounds here where the user will
             experience a slight UI jolt, but this heuristic mostly
             seems to work out okay. If there was no previous message,
             assume we don't have any messages yet and go ahead and
             scroll this message into view (noting that that scrolling
             is hypothetically a no-op in such cases).

             The wrench in these works are posts with IMG tags, as
             those images are loaded async and the element does not
             yet have enough information to know how far to scroll!
             For such cases we have to delay the scroll until the
             image loads (and we hope it does so before another
             message arrives).
          */
          if(1===+e.dataset.hasImage){
            e.querySelector('img').addEventListener('load',()=>e.scrollIntoView());
          }else if(!prevMessage || (prevMessage && isInViewport(prevMessage))){
            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
         footer, leaving only the chat application visible to the
         user.
      */
      chatOnlyMode: function f(yes){
        if(undefined === f.elemsToToggle){
          f.elemsToToggle = [];
          document.querySelectorAll(
            ["body > div.header",
            "body > div.header, body > div.mainmenu, body > div.footer"
             "body > div.mainmenu",
             "body > div.footer",
             "#debugMsg"
            ].join(',')
          ).forEach((e)=>f.elemsToToggle.push(e));
        }
        if(!arguments.length) yes = true;
        if(yes === this.isChatOnlyMode()) return this;
        if(yes){
          D.addClass(f.elemsToToggle, 'hidden');
          D.addClass(document.body, 'chat-only-mode');

      return qs('[data-msgid="'+id+'"]');
    };

    /** Finds the last .message-widget element and returns it or
        the undefined value if none are found. */
    cs.fetchLastMessageElem = function(){
      const msgs = document.querySelectorAll('.message-widget');
      var rc;
      if(msgs.length){
      return msgs.length ? msgs[msgs.length-1] : undefined;
        rc = this.e.newestMessage = msgs[msgs.length-1];
      }
      return rc;
    };

    /**
       LOCALLY deletes a message element by the message ID or passing
       the .message-row element. Returns true if it removes an element,
       else false.
    */
    cs.deleteMessageElem = function(id){
      var e;
      if(id instanceof HTMLElement){
        e = id;
        id = e.dataset.msgid;
      }else{
        e = this.getMessageElemById(id);
      }
      if(e && id){
        D.remove(e);
        if(e===this.newestMessageElem){
          Chat.newestMessageElem = Chat.fetchLastMessageElem();
        if(e===this.e.newestMessage){
          this.fetchLastMessageElem();
        }
        F.toast.message("Deleted message "+id+".");
      }
      return !!e;
    };

    /** Given a .message-row element, this function returns whethe the

        var contentTarget = this.e.content;
        if( m.fsize>0 ){
          if( m.fmime
              && m.fmime.startsWith("image/")
              && Chat.settings.getBool('images-inline',true)
            ){
            contentTarget.appendChild(D.img("chat-download/" + m.msgid));
            ds.hasImage = 1;
          }else{
            const a = D.a(
              window.fossil.rootPath+
                'chat-download/' + m.msgid+'/'+encodeURIComponent(m.fname),
              // ^^^ add m.fname to URL to cause downloaded file to have that name.
              "(" + m.fname + " " + m.fsize + " bytes)"
            )

    /* ^^^ we don't use Chat.reportError(e) here b/c the polling
       fails exepectedly when it times out, but is then immediately
       resumed, and reportError() produces a loud error message. */
      .finally(function(){
        if(isFirstCall){
          Chat.isMassLoading = false;
          Chat.ajaxEnd();
          setTimeout(function(){
            const m = Chat.newestMessageElem;
            if(m){
          const m = Chat.e.newestMessage;
          if(m) Chat.scheduleScrollOfMsg(m);
              m.scrollIntoView();
              //console.debug("Scrolling into view...",msgs[msgs.length-1]);
            }
            Chat.e.inputWrapper.scrollIntoView()
          setTimeout(()=>Chat.e.inputWrapper.scrollIntoView(), 0);
          }, 0);
        }
        poll.running=false;
      });
  }
  poll.running = false;
  poll(true);
  setInterval(poll, 1000);
  F.page.chat = Chat/* enables testing the APIs via the dev tools */;
})();