code: function (data, context) {
              if (!data) {
                  return;
              }
  
              var relativeFilename = FileUtils.getRelativeFilename(this.prefFilePath, context[this.key]);
  
              if (relativeFilename) {
                  var glob = _findMatchingGlob(data, relativeFilename);
                  if (glob) {
                      return _.keys(data[glob]);
                  } else {
                      return [];
                  }
              }
              return _.union.apply(null, _.map(_.values(data), _.keys));
          }
docs: Retrieves the keys provided by this layer object. If context with a filename is provided,
  only the keys for the matching file glob are given. Otherwise, all keys for all globs
  are provided.
  
  @param {Object} data the preference data from the Scope
  @param {?Object} context Additional context data (filename in particular is important)