docs: function processFile(md) {
    return (file, callback) => {
      let content;
      let footnotes;
      try {
        const tokens = md.parse(file.meta.content, {});
        const footnoteTokens = popFootnoteTokens(tokens);
        footnotes = footnoteTokensToMeta(footnoteTokens, md);
        content = md.renderer.render(tokens, md.options, {});
      } catch (error) {
        console.error(`${file.path}: Could not render the content`);
        async.nextTick(callback, error);
        return;
      }
  
      const meta = Object.assign({}, file.meta, { content, footnotes });
      async.nextTick(callback, null, Object.assign({}, file, { meta }));
    };
  }