code: function registerLangHandler(handler, fileExtensions) {
      for (var i = fileExtensions.length; --i >= 0;) {
        var ext = fileExtensions[i];
        if (!langHandlerRegistry.hasOwnProperty(ext)) {
          langHandlerRegistry[ext] = handler;
        } else if (win['console']) {
          console['warn']('cannot override language handler %s', ext);
        }
      }
    }
docs: Register a language handler for the given file extensions.
  @param {function (JobT)} handler a function from source code to a list
  of decorations.  Takes a single argument job which describes the
  state of the computation and attaches the decorations to it.
  @param {Array.<string>} fileExtensions