const tdLn = tbl.querySelector('td.line-numbers');
  const urlArgsRaw = (window.location.search||'?')
      .replace(/&?\budc=[^&]*/,'') /* "update display prefs cookie" */
      .replace(/&?\bln=[^&]*/,'') /* inbound line number/range */
      .replace('?&','?');
  const lineState = { urlArgs: urlArgsRaw, start: 0, end: 0 };
  const lineTip = new F.PopupWidget({
    style: {
      cursor: 'pointer'
    },
    refresh: function(){
      const link = this.state.link;
      D.clearElement(link);
      if(lineState.start){
        const ls = [lineState.start];
        if(lineState.end) ls.push(lineState.end);
        link.dataset.url = (

        );
      }else{
        D.append(link, "No lines selected.");
      }
    },
    init: function(){
      const e = this.e;
      const btnCopy = D.span(),
            link = D.span();
      const btnCopy = D.attr(D.button(), 'id', 'linenum-copy-button');
            link = D.label('linenum-copy-button');
      this.state = {link};
      F.copyButton(btnCopy,{
        copyFromElement: link,
        extractText: ()=>link.dataset.url,
        oncopy: (ev)=>{
          D.flashOnce(ev.target, undefined, ()=>lineTip.hide());
          setTimeout(()=>lineTip.hide(), 400);
          // arguably too snazzy: F.toast.message("Copied link to clipboard.");
        }
      });
      this.e.addEventListener('click', ()=>btnCopy.click(), false);
      D.append(this.e, btnCopy, link)
      D.append(this.e, btnCopy, link);
    }
  });

  tbl.addEventListener('click', ()=>lineTip.hide(), true);
  
  tdLn.addEventListener('click', function f(ev){
    if('SPAN'!==ev.target.tagName) return;