Style guide says enum values should be lowerCamelCase.

sky/sdk/lib/framework/components2/checkbox.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import '../fn2.dart';
 import 'button_base.dart';
 import 'dart:sky' as sky;
 
 typedef void ValueChanged(value);
 
@@ skipping 50 matching lines @@
   Checkbox({ Object key, this.onChanged, this.checked }) : super(key: key);
 
   void _handleClick(sky.Event e) {
     onChanged(!checked);
   }
 
   UINode buildContent() {
     return new EventListenerNode(
       new FlexContainer(
         style: _style,
-        direction: FlexDirection.Row,
+        direction: FlexDirection.horizontal,
         children: [
           new Container(
             style: highlight ? _containerHighlightStyle : _containerStyle,
             children: [
               new Container(
                 style: checked ? _checkedStyle : _uncheckedStyle
               )
             ]
           )
         ]
       ),
       onGestureTap: _handleClick
     );
   }
 }