src/language-js/embed.js/isMarkdown
function isMarkdown(path) {
  const node = path.getValue();
  const parent = path.getParentNode();
  return (
    parent &&
    parent.type === "TaggedTemplateExpression" &&
    node.quasis.length === 1 &&
    parent.tag.type === "Identifier" &&
    (parent.tag.name === "md" || parent.tag.name === "markdown")
  );
}