src/language-html/print/tag.js/printOpeningTagStartMarker
function printOpeningTagStartMarker(node) {
  switch (node.type) {
    case "ieConditionalComment":
    case "ieConditionalStartComment":
      return `<!--[if ${node.condition}`;
    case "ieConditionalEndComment":
      return "<!--<!";
    case "interpolation":
      return "{{";
    case "docType":
      return "<!DOCTYPE";
    case "element":
      if (node.condition) {
        return `<!--[if ${node.condition}]><!--><${node.rawName}`;
      }
    // fall through
    default:
      return `<${node.rawName}`;
  }
}