code: function (descriptor) {
          var result = {};
          for (var key in descriptor) {
              if (Object.prototype.hasOwnProperty.call(descriptor, key)) {
                  var keys = key.split(',');
                  for (var i = 0, len = keys.length; i < len; i += 1) {
                      var method = keys[i];
                      if (!ACCEPTABLE_METHOD_SET[method]) {
                          throw new Error("Unknown descriptor method " + method);
                      }
                      if (Object.prototype.hasOwnProperty.call(result, method)) {
                          throw new Error("Already specified descriptor method " + method);
                      }
                      result[method] = descriptor[key];
                  }
              }
          }
          if (!result.options) {
              result.options = createOptionsHandler(result);
          }
          return freeze(result);
      }
docs: Verify the validity of the provided descriptor and return a sanitized version.
  This will add an options handler if none is provided.
  
  @param {Object} descriptor A map of methods to their associated callbacks
  @return {Object} A map of methods to their associated callbacks
  @api private
  
  @example descriptor = sanitizeDescriptor(descriptor);