src/language-html/print/tag.js/printClosingTagStartMarker
function printClosingTagStartMarker(node, options) {
  assert(!node.isSelfClosing);
  /* istanbul ignore next */
  if (shouldNotPrintClosingTag(node, options)) {
    return "";
  }
  switch (node.type) {
    case "ieConditionalComment":
      return "<!";
    case "element":
      if (node.hasHtmComponentClosingTag) {
        return "<//";
      }
    // fall through
    default:
      return `</${node.rawName}`;
  }
}