code: function editArticleInPart(part, level, newArticle) {
      var articles = part.getArticles();
      articles = editArticleInList(articles, level, newArticle);
  
      return part.set('articles', articles);
  }
docs: Edit an article in a part
  
  @param {Part} part
  @param {String} level
  @param {Article} newArticle
  @return {Part}