if(!e){
      e = new Error("Cannot find DOM element: "+x);
      console.error(e, src);
      throw e;
    }
    return e;
  };

  /**
     "Blinks" the given element a single time for the given number of
     milliseconds, defaulting to flashOnce.defaultTimeMs. This will
     only activate once per element during that timeframe - further
     calls will become no-ops until the blink is completed. This
     routine adds a dataset member to the element for the duration of
     the blink, to allow it to block multiple blinks.

     Returns e.
  */
  dom.flashOnce = function f(e,howLongMs){
    if(e.dataset.isBlinking){
      return;
    }
    if(!howLongMs || 'number'!==typeof howLongMs){
      howLongMs = f.defaultTimeMs;
    }
    e.dataset.isBlinking = true;
    const transition = e.style.transition;
    e.style.transition = "opacity "+howLongMs+"ms ease-in-out";
    const opacity = e.style.opacity;
    e.style.opacity = 0;
    setTimeout(function(){
      e.style.transition = transition;
      e.style.opacity = opacity;
      delete e.dataset.isBlinking;
    }, howLongMs);
    return e;
  };
  dom.flashOnce.defaultTimeMs = 400;

  /**
     Attempts to copy the given text to the system clipboard.  Returns
     true if it succeeds, else false.
  */
  dom.copyTextToClipboard = function(text){
    if( window.clipboardData && window.clipboardData.setData ){
      clipboardData.setData('Text',text);
      return true;
    }else{
      const x = document.createElement("textarea");
      x.style.position = 'fixed';
      x.value = text;
      document.body.appendChild(x);
      x.select();
      var rc;
      try{
        document.execCommand('copy');
        rc = true;
      }catch(err){
        rc = false;
      }finally{
        document.body.removeChild(x);
      }
      return rc;
    }
  };

  return F.dom = dom;
})(window.fossil);