docs: function helper(app, file, key, re) {
    var h = get(app._.asyncHelpers, key);
    var a = get(app._.helpers, key);
  
    if (!h && !a) {
      set(file.data, key, function () {
        return comment(key, 'helper');
      });
  
      if (re.test(file.content)) {
        var message = 'MISSING helper: "' + key + '".\n';
        // rethrow (or actually throw) the error
        var err = new SyntaxError(message);
        if (app.disabled('silent')) {
          rethrow(err, file.path, file.content, re);
        }
      }
    }
  }