// truncation off the right edge of the page.
      const pRect = f.popup.e.getBoundingClientRect();
      x -= pRect.width/3*2;
    }
    f.popup.show(x, y);
  };

  /**
     Parses the given chat message string for hyperlinks and @NAME
     references, replacing them with markup, then stuffs the parsed
     content into the given target DOM element.

     This is an intermediary step until we get some basic markup
     support coming from the server side.
  */
  const messageToDOM = function f(str, tgtElem){
    "use strict";
    if(!f.rxUrl){
      f.rxUrl = /\b(?:https?|ftp):\/\/[a-z0-9-+&@#\/%?=~_|!:,.;]*[a-z0-9-+&@#\/%=~_|]/gim;
      f.rxAt = /@\w+/gmi;
      f.rxNS = /\S/;
      f.ce = (T)=>document.createElement(T);
      f.ct = (T)=>document.createTextNode(T);
      f.replaceUrls = function ff(sub, offset, whole){
        if(offset > ff.prevStart){
          f.accum.push((ff.prevStart?' ':'')+whole.substring(ff.prevStart, offset-1)+' ');
        }
        const a = f.ce('a');
        a.setAttribute('href',sub);
        a.setAttribute('target','_blank');
        a.appendChild(f.ct(sub));
        f.accum.push(a);
        ff.prevStart = offset + sub.length + 1;
      };
      f.replaceAtName = function ff(sub, offset,whole){
        if(offset > ff.prevStart){
          ff.accum.push((ff.prevStart?' ':'')+whole.substring(ff.prevStart, offset-1)+' ');
        }else if(offset && f.rxNS.test(whole[offset-1])){
          // Sigh: https://stackoverflow.com/questions/52655367
          ff.accum.push(sub);
          return;
        }
        const e = f.ce('span');
        e.classList.add('at-name');
        e.appendChild(f.ct(sub));
        ff.accum.push(e);
        ff.prevStart = offset + sub.length + 1;
      };
    }
    f.accum = []; // accumulate strings and DOM elements here.
    f.rxUrl.lastIndex = f.replaceUrls.prevStart = 0; // reset regex cursor
    str.replace(f.rxUrl, f.replaceUrls);
    // Push remaining non-URL part of the string to the queue...
    if(f.replaceUrls.prevStart < str.length){
      f.accum.push((f.replaceUrls.prevStart?' ':'')+str.substring(f.replaceUrls.prevStart));
    }
    // Pass 2: process @NAME references...
    // TODO: only match NAME if it's the name of a currently participating
    // user. Add a second class if NAME == current user, and style that one
    // differently so that people can more easily see when they're spoken to.
    const accum2 = f.replaceAtName.accum = [];
    f.accum.forEach(function(v){
      if('string'===typeof v){
        f.rxAt.lastIndex = f.replaceAtName.prevStart = 0;
        v.replace(f.rxAt, f.replaceAtName);
        if(f.replaceAtName.prevStart < v.length){
          accum2.push((f.replaceAtName.prevStart?' ':'')+v.substring(f.replaceAtName.prevStart));
        }
      }else{
        accum2.push(v);
      }
    });
    delete f.accum;
    const theTgt = tgtElem || f.ce('div');
    const strings = [];
    accum2.forEach(function(e){
      if('string'===typeof e) strings.push(e);
      else strings.push(e.outerHTML);
    });
    D.parseHtml(theTgt, strings.join(''));
    return theTgt;
  }/*end messageToDOM()*/;

  /** Callback for poll() to inject new content into the page. */
  function newcontent(jx){
    var i;
    if('visible'===document.visibilityState){
      if(Chat.changesSincePageHidden){
        Chat.changesSincePageHidden = 0;
        Chat.pageTitle.innerText = Chat.pageTitleOrig;

          ));
        }
        const br = D.br();
        br.style.clear = "both";
        eContent.appendChild(br);
      }
      if(m.xmsg){
        // The m.xmsg text comes from the same server as this script and
        // is guaranteed by that server to be "safe" HTML - safe in the
        // 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.
        messageToDOM(m.xmsg, eContent);
        eContent.innerHTML += m.xmsg
      }
      eContent.classList.add('chat-message');
    }
  }
  async function poll(){
    if(poll.running) return;
    poll.running = true;