** list of objects.
*/
void chat_send_webpage(void){
  int nByte;
  const char *zMsg;
  const char *zUserName;
  login_check_credentials();
  if( 0==g.perm.Chat ) {
    chat_emit_permissions_error(0);
    return;
  }
  chat_create_tables();
  zUserName = (g.zLogin && g.zLogin[0]) ? g.zLogin : "nobody";
  nByte = atoi(PD("file:bytes","0"));
  zMsg = PD("msg","");

     Returns an almost-ISO8601 form of Date object d.
  */
  const iso8601ish = function(d){
    return d.toISOString()
        .replace('T',' ').replace(/\.\d+/,'')
        .replace('Z', ' zulu');
  };
  const pad2 = (x)=>('0'+x).substr(-2);
  /** Returns the local time string of Date object d, defaulting
      to the current time. */
  const localTimeString = function ff(d){
    d || (d = new Date());
    return [
      d.getFullYear(),'-',pad2(d.getMonth()+1/*sigh*/),
      '-',pad2(d.getDate()),

    };
    /**
       Reports an error in the form of a new message in the chat
       feed. All arguments are appended to the message's content area
       using fossil.dom.append(), so may be of any type supported by
       that function.
    */
    cs.reportErrorAsMessage = function f(/*msg args*/){
      if(undefined === f.$msgid) f.$msgid=0;
      const args = argsToArray(arguments).map(function(v){
        return (v instanceof Error) ? v.message : v;
      });
      console.error("chat error:",args);
      const d = new Date().toISOString(),
            mw = new this.MessageWidget({
              isError: true,
              xfrom: null,
              msgid: "error-"+(++f.$msgid),
              mtime: d,
              lmtime: d,
              xmsg: args
            });
      this.injectMessageElem(mw.e.body);
      mw.scrollIntoView();
    };

        cs.setUserFilter(uname);
      }
      return false;
    }, false);
    return cs;
  })()/*Chat initialization*/;


  /** Returns the first .message-widget element in DOM element
      e's lineage. */
  const findMessageWidgetParent = function(e){
    while( e && !e.classList.contains('message-widget')){
      e = e.parentNode;
    }
    return e;
  };

  /**
     Custom widget type for rendering messages (one message per
     instance). These are modelled after FIELDSET elements but we
     don't use FIELDSET because of cross-browser inconsistencies in
     features of the FIELDSET/LEGEND combination, e.g. inability to
     align legends via CSS in Firefox and clicking-related
     deficiencies in Safari.

      D.append(this.e.body, this.e.tab, this.e.content);
      this.e.tab.setAttribute('role', 'button');
      if(arguments.length){
        this.setMessage(arguments[0]);
      }
    };
    /* Left-zero-pad a number to at least 2 digits */

    const dowMap = {
      /* Map of Date.getDay() values to weekday names. */
      0: "Sunday", 1: "Monday", 2: "Tuesday",
      3: "Wednesday", 4: "Thursday", 5: "Friday",
      6: "Saturday"
    };
    /* Given a Date, returns the timestamp string used in the
       "tab" part of message widgets. */
    const theTime = function(d){
      return [
        //d.getFullYear(),'-',pad2(d.getMonth()+1/*sigh*/),
        //'-',pad2(d.getDate()), ' ',
        d.getHours(),":",
        (d.getMinutes()+100).toString().slice(1,3),
        ' ', dowMap[d.getDay()]
      ].join('');
    };

    cf.prototype = {
      scrollIntoView: function(){
        this.e.content.scrollIntoView();
      },
      setMessage: function(m){
        const ds = this.e.body.dataset;
        ds.timestamp = m.mtime;

        }else{/*notification*/
          D.addClass(this.e.body, 'notification');
          if(m.isError){
            D.addClass([contentTarget, this.e.tab], 'error');
          }
          D.append(
            this.e.tab,
            D.append(D.code(), 'notification @ ',theTime(d))
          );
        }
        if( m.xfrom && m.fsize>0 ){
          if( m.fmime
              && m.fmime.startsWith("image/")
              && Chat.settings.getBool('images-inline',true)
            ){

          // sense that it is not possible for a malefactor to inject HTML
          // or javascript or CSS.  The m.xmsg content might contain
          // hyperlinks, but otherwise it will be markup-free.  See the
          // chat_format_to_html() routine in the server for details.
          //
          // Hence, even though innerHTML is normally frowned upon, it is
          // perfectly safe to use in this context.
          if(m.xmsg && 'string' !== typeof m.xmsg){
            // Used by Chat.reportErrorAsMessage()
            D.append(contentTarget, m.xmsg);
          }else{
            contentTarget.innerHTML = m.xmsg;
            contentTarget.querySelectorAll('a').forEach(addAnchorTargetBlank);
            if(F.pikchr){
              F.pikchr.addSrcView(contentTarget.querySelectorAll('svg.pikchr'));
            }
          }
        }
        //console.debug("tab",this.e.tab);
        //console.debug("this.e.tab.firstElementChild",this.e.tab.firstElementChild);
        this.e.tab.firstElementChild.addEventListener('click', this._handleLegendClicked, false);
        /*if(eXFrom){
          eXFrom.addEventListener('click', ()=>this.e.tab.click(), false);
        }*/
        return this;
      },
      /* Event handler for clicking .message-user elements to show their

                return;
              }
              this.$eMsg = tgtMsg;
              this.refresh();
            }
          }/*f.popup*/;
        }/*end static init*/
        const theMsg = findMessageWidgetParent(ev.target);



        if(theMsg) f.popup.show(theMsg);
      }/*_handleLegendClicked()*/
    };
    return cf;
  })()/*MessageWidget*/;

  const BlobXferState = (function(){
    /* State for paste and drag/drop */
    const bxs = {
      dropDetails: document.querySelector('#chat-drop-details'),
      blob: undefined,
      clear: function(){
        this.blob = undefined;
        D.clearElement(this.dropDetails);
        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 = bxs.updateDropZoneContent = function(blob){
      //console.debug("updateDropZoneContent()",blob);
      const dd = bxs.dropDetails;
      bxs.blob = blob;
      D.clearElement(dd);
      if(!blob){
        Chat.e.inputFile.value = '';
        return;

    return bxs;
  })()/*drag/drop/paste*/;

  const tzOffsetToString = function(off){
    const hours = Math.round(off/60), min = Math.round(off % 30);
    return ''+(hours + (min ? '.5' : ''));
  };

  const localTime8601 = function(d){
    return [
      d.getYear()+1900, '-', pad2(d.getMonth()+1), '-', pad2(d.getDate()),
      'T', pad2(d.getHours()),':', pad2(d.getMinutes()),':',pad2(d.getSeconds())
    ].join('');
  };

  /**
     Called by Chat.submitMessage() when message sending failed. Injects a fake message
     containing the content and attachment of the failed message and gives the user buttons
     to discard it or edit and retry.
   */
  const recoverFailedMessage = function(state){
    const w = D.addClass(D.div(), 'failed-message');
    D.append(w, D.append(
      D.span(),"This message was not successfully sent to the server:"
    ));
    if(state.msg){
      const ta = D.textarea();
      ta.value = state.msg;
      D.append(w,ta);
    }
    if(state.blob){
      D.append(w,D.append(D.span(),"Attachment: ",(state.blob.name||"unnamed")));
      //console.debug("blob = ",state.blob);
    }
    const buttons = D.addClass(D.div(), 'buttons');
    D.append(w, buttons);
    D.append(buttons, D.button("Discard message?", function(){
      let theMsg = findMessageWidgetParent(w);
      if(theMsg) Chat.deleteMessageElem(theMsg);
    }));
    D.append(buttons, D.button("Edit message and try again?", function(){
      if(state.msg) Chat.inputValue(ta.value);
      if(state.blob) BlobXferState.updateDropZoneContent(state.blob);
      let theMsg = findMessageWidgetParent(w);
      if(theMsg) Chat.deleteMessageElem(theMsg);
    }));
    Chat.reportErrorAsMessage(w);
  };

  /**
     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+$/;
      f.markdownContinuation = /\\\s+$/;
    }
    this.setCurrentView(this.e.viewMessages);
    const fd = new FormData();
    const fallback = {msg: this.inputValue()};
    var msg = fallback.msg.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

      });
      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;
    fallback.blob = file;
    const self = this;
    fd.set("lmtime", localTime8601(new Date()));
    F.fetch("chat-send",{
      payload: fd,
      responseType: 'text',
      onerror:function(err){
        self.reportErrorAsMessage(err);
        recoverFailedMessage(fallback);
      },
      onload:function(txt){
        if(!txt) return/*success response*/;
        try{
          const json = JSON.parse(txt);
          self.newContent({msgs:[json]});
        }catch(e){
          self.reportError(e);

        }
        recoverFailedMessage(fallback);
      }
    });
    BlobXferState.clear();
    Chat.inputValue("").inputFocus();
  };

  const inputWidgetKeydown = function f(ev){

}
body.chat .message-widget-content > .markdown > *:first-child {
  margin-top: 0;
}
body.chat .message-widget-content > .markdown > *:last-child {
  margin-bottom: 0;
}
body.chat .message-widget-content.error .buttons {
  display: flex;
  flex-direction: row;
  justify-content: space-around;
  flex-wrap: wrap;
}
body.chat .message-widget-content.error .buttons > button {
  margin: 0.25em;
}

body.chat .message-widget-content.error a {
  color: inherit;
}
body.chat .message-widget-content.error .failed-message {
  display: flex;
  flex-direction: column;
}
body.chat .message-widget-content.error .failed-message textarea {
  min-height: 5rem;
}

/* User name and timestamp (a LEGEND-like element) */
body.chat .message-widget .message-widget-tab {
  border-radius: 0.25em 0.25em 0 0;
  margin: 0 0.25em 0em 0.15em;
  padding: 0 0.5em 0.15em 0.5em;
  cursor: pointer;
  white-space: nowrap;

<title>Change Log</title>

<h2 id='v2_18'>Changes for version 2.18 (pending)</h2>
  *  [/help?cmd=/chat|The /chat page] input options have been reworked
     again for better cross-browser portability.
  *  When sending a [/help?cmd=/chat|/chat] message fails, it is no longer
     immediately lost and sending may optionally be retried.

<h2 id='v2_17'>Changes for version 2.17 (2021-10-09)</h2>

  *  Major improvements to the "diff" subsystem, including: <ul>
     <li> Added new [/help?cmd=diff|formatting options]: --by, -b, --webpage, --json, --tcl.
     <li> Partial-line matching for unified diffs
     <li> Better partial-line matching for side-by-side diffs