old_contents: import Orbit from 'orbit/core';
  import Evented from 'orbit/evented';
  
  var Transformable = {
    extend: function(object, actions) {
      if (object._requestable === undefined) {
        this._requestable = true;
  
        Evented.extend(object);
  
        object.didTransform = function(diff, result) {
          return object.settle.call(object, 'didTransform', diff, result);
        };
  
        object.transform = function(diff) {
          Orbit.assert('_transform must be defined', object._transform);
  
          return object._transform.call(object, diff).then(
            function(result) {
              return object.didTransform.call(object, diff, result).then(
                function() {
                  return result;
                }
              );
            },
            function(error) {
              return object.settle.call(object, 'didNotTransform', diff, error).then(
                function() {
                  throw error;
                }
              );
            }
          );
        };
      }
      return object;
    }
  };
  
  export default Transformable;
new_contents: import Orbit from 'orbit/core';
  import Evented from 'orbit/evented';
  
  var Transformable = {
    extend: function(object, actions) {
      if (object._requestable === undefined) {
        this._requestable = true;
  
        Evented.extend(object);
  
        object.didTransform = function(operation, result) {
          return object.settle.call(object, 'didTransform', operation, result);
        };
  
        object.transform = function(operation) {
          Orbit.assert('_transform must be defined', object._transform);
  
          return object._transform.call(object, operation).then(
            function(result) {
              return object.didTransform.call(object, operation, result).then(
                function() {
                  return result;
                }
              );
            },
            function(error) {
              return object.settle.call(object, 'didNotTransform', operation, error).then(
                function() {
                  throw error;
                }
              );
            }
          );
        };
      }
      return object;
    }
  };
  
  export default Transformable;
subject: Rename `diff` -> `operation`