src/language-html/conditional-comment.js/parseIeConditionalStartComment
function parseIeConditionalStartComment(node, parseHtml, match) {
  const [, condition] = match;
  return {
    type: "ieConditionalStartComment",
    condition: condition.trim().replace(/\s+/g, " "),
    sourceSpan: node.sourceSpan,
  };
}