code: function fixOutputPaths(output, files) {
  
      // map directories to use for index files
      var dirMap = {};
      u.each(files, function(file) {
        dirMap[ppath.dirname(file.path)] = true;
  
        // edge case - treat /foo/ as directory too
        if (/\/$/.test(file.path) && ppath.dirname(file.path) !== file.path) {
          dirMap[file.path] = true;
        }
      });
  
      // default output file extension is .html
      var extension = 'extension' in output ? (output.extension || '') : '.html';
      var indexFile = output.indexFile || 'index';
  
      u.each(files, function(file) {
        if (dirMap[file.path]) {
          debug('index file for %s', file.path);
          file.path = ppath.join(file.path, indexFile);
        }
        if (!/\.[^/]*$/.test(file.path)) {
          file.path = file.path + extension;
        }
      });
    }
docs: convert file-paths to 'index' files where necessary