Chat.e.inputFile.value = "";
      }
    };
    /** Updates the paste/drop zone with details of the pasted/dropped
        data. The argument must be a Blob or Blob-like object (File) or
        it can be falsy to reset/clear that state.*/
    const updateDropZoneContent = function(blob){
      //console.debug("updateDropZoneContent()",blob);
      const dd = bxs.dropDetails;
      bxs.blob = blob;
      D.clearElement(dd);
      if(!blob){
        Chat.e.inputFile.value = '';
        return;
      }

     Submits the contents of the message input field (if not empty)
     and/or the file attachment field to the server. If both are
     empty, this is a no-op.
  */
  Chat.submitMessage = function f(){
    if(!f.spaces){
      f.spaces = /\s+$/;
      f.markdownContinuation = /\\\s\s$/;
    }
    this.setCurrentView(this.e.viewMessages);
    const fd = new FormData();
    var msg = this.inputValue().trim();
    if(msg && (msg.indexOf('\n')>0 || f.spaces.test(msg))){
      /* Cosmetic: trim whitespace from the ends of lines to try to
         keep copy/paste from terminals, especially wide ones, from
         forcing a horizontal scrollbar on all clients. This breaks
         markdown's use of blackslash-space-space for paragraph
         continuation, but *not* doing this affects all clients every
         time someone pastes in console copy/paste from an affected
         platform. */
      const xmsg = msg.split('\n');
      xmsg.forEach(function(line,ndx){
        if(!f.markdownContinuation.test(line)){
          xmsg[ndx] = line.trimRight();
        }
      });
      msg = xmsg.join('\n');
    }
    if(msg) fd.set('msg',msg);
    const file = BlobXferState.blob || this.e.inputFile.files[0];
    if(file) fd.set("file", file);
    if( !msg && !file ) return;

       fired via Chat.settings.set() so that the checkbox can stay in
       sync with external changes to that setting. Various Chat UI
       elements stay in sync with the config UI via those settings
       events.
     */
    const settingsOps = [{
      label: "Ctrl-enter to Send",
      hint: "When on, only Ctrl-Enter will send messages and Enter adds "+
        "blank lines. "+
        "When off, both Enter and Ctrl-Enter send. "+
        "When the input field has focus, is empty, and preview "+
        "mode is NOT active then Ctrl-Enter toggles this setting.",
      boolValue: 'edit-ctrl-send'
    },{
      label: "Compact mode",
      hint: "Toggle between a space-saving and more spacious writing area. "+

          /* Missing file - removed after this setting was
            applied. Fall back to the first sound in the list. */
          selectSound.selectedIndex = firstSoundIndex;
        }
      }
      Chat.setNewMessageSound(selectSound.value);
      settingsOps.push({

        hint: "Audio alert. How to enable audio playback is browser-specific!",
        select: selectSound,
        callback: function(ev){
          const v = ev.target.value;
          Chat.setNewMessageSound(v);
          F.toast.message("Audio notifications "+(v ? "enabled" : "disabled")+".");
          if(v) setTimeout(()=>Chat.playNewMessageSound(), 0);
        }
      });
    }/*audio notification config*/
    /**
       Build UI for config options...
    */
    settingsOps.forEach(function f(op){
      const line = D.addClass(D.div(), 'menu-entry');
      const label = op.label ? D.append(
        D.addClass(D.label(), 'cbutton'/*bootstrap skin hijacks 'button'*/),
        op.label) : undefined;
      const labelWrapper = D.addClass(D.div(), 'label-wrapper');
      var hint;
      const col0 = D.span();
      if(op.hint){
        hint = D.append(D.addClass(D.span(),'hint'),op.hint);
      }
      if(op.hasOwnProperty('select')){
        D.append(line, col0, labelWrapper);
        D.append(labelWrapper, op.select);
        if(hint) D.append(labelWrapper, hint);
        if(label) D.append(col0, label);
        if(op.callback){
          op.select.addEventListener('change', (ev)=>op.callback(ev), false);
        }
      }else if(op.hasOwnProperty('boolValue')){
        if(undefined === f.$id) f.$id = 0;
        ++f.$id;
        if('string' ===typeof op.boolValue){
          const key = op.boolValue;
          op.boolValue = ()=>Chat.settings.getBool(key);
          op.persistentSetting = key;
        }
        const check = op.checkbox
              = D.attr(D.checkbox(1, op.boolValue()),
                       'aria-label', op.label);
        const id = 'cfgopt'+f.$id;
        check.checked = op.boolValue();
        op.checkbox = check;
        D.attr(check, 'id', id);

        D.append(line, col0, labelWrapper);
        D.append(col0, check);
        if(label){
          D.attr(label, 'for', id);
          D.append(labelWrapper, label);
        }
        if(hint) D.append(labelWrapper, hint);
      }else{
        line.addEventListener('click', callback);
        D.append(line, col0, labelWrapper);
        if(label) D.append(labelWrapper, label);
        if(hint) D.append(labelWrapper, hint);
      }
      D.append(optionsMenu, line);
      if(op.persistentSetting){
        Chat.settings.addListener(
          op.persistentSetting,
          function(setting){
            if(op.checkbox) op.checkbox.checked = !!setting.value;