code: function(div) {
    var sizeSpan = document.createElement('span');
    sizeSpan.setAttribute('style', 'margin: 0; padding: 0 0 0 1em; border: 0;');
    div.appendChild(sizeSpan);
    var oneEmWidth=sizeSpan.offsetWidth;
    div.removeChild(sizeSpan);
    return oneEmWidth;
  }
docs: Needed for dashed lines.