docs: function orderColumns() {
          var keyTotals = filenames.reduce(reduceFilenamesToKeyTotal, {});
          return sort(keyTotals);
  
          function reduceFilenamesToKeyTotal(reduced, filename) {
            var item = json[filename];
            return Object.keys(item)
              .reduce(reducePropToLength.bind(item), reduced);
          }
        }