code: function removeArticle(summary, level) {
      // Coerce to level
      level = is.string(level)? level : level.getLevel();
  
      var parent = summary.getParent(level);
  
      var articles = parent.getArticles();
      // Find the index to remove
      var index = articles.findIndex(function(art) {
          return art.getLevel() === level;
      });
      if (index === -1) {
          return summary;
      }
  
      // Remove from children
      articles = articles.remove(index);
      parent = parent.set('articles', articles);
  
      // Reindex the level from here
      parent = indexArticleLevels(parent);
  
      return mergeAtLevel(summary, parent.getLevel(), parent);
  }
docs: Remove an article from a level.
  
  @param {Summary} summary
  @param {String|SummaryArticle} level: level to remove
  @return {Summary}