src/language-css/parser-postcss.js/parseWithParser
function parseWithParser(parser, text, frontMatter) {
  let result;
  try {
    result = parser.parse(text);
  } catch (e) {
    if (typeof e.line !== "number") {
      throw e;
    }
    throw createError("(postcss) " + e.name + " " + e.reason, { start: e });
  }

  if (Object.keys(frontMatter.data).length > 0) {
    result.nodes.unshift({
      type: "comment-yaml",
      value: grayMatter.stringify("", frontMatter.data).replace(/\s$/, "")
    });
  }

  const prefixedResult = addTypePrefix(result, "css-");
  const parsedResult = parseNestedCSS(prefixedResult);
  return parsedResult;
}