code: function positiveSize(e) {
      var rect = bot.dom.getClientRect(e);
      if (rect.height > 0 && rect.width > 0) {
        return true;
      }
      // A vertical or horizontal SVG Path element will report zero width or
      // height but is "shown" if it has a positive stroke-width.
      if (bot.dom.isElement(e, 'PATH') && (rect.height > 0 || rect.width > 0)) {
        var strokeWidth = bot.dom.getEffectiveStyle(e, 'stroke-width');
        return !!strokeWidth && (parseInt(strokeWidth, 10) > 0);
      }
      // Zero-sized elements should still be considered to have positive size
      // if they have a child element or text node with positive size, unless
      // the element has an 'overflow' style of 'hidden'.
      return bot.dom.getEffectiveStyle(e, 'overflow') != 'hidden' &&
          goog.array.some(e.childNodes, function(n) {
            return n.nodeType == goog.dom.NodeType.TEXT ||
                   (bot.dom.isElement(n) && positiveSize(n));
          });
    }
docs: Any element without positive size dimensions is not shown.