docs: function getCoverPath(output) {
      var outputRoot = output.getRoot();
      var book = output.getBook();
      var config = book.getConfig();
      var coverName = config.getValue('cover', 'cover.jpg');
  
      // Resolve to absolute
      var cover = fs.pickFile(outputRoot, coverName);
      if (cover) {
          return cover;
      }
  
      // Multilingual? try parent folder
      if (book.isLanguageBook()) {
          cover = fs.pickFile(path.join(outputRoot, '..'), coverName);
      }
  
      return cover;
  }