Style guide says enum values should be lowerCamelCase.

sky/sdk/lib/framework/layout.dart

 library layout;
 
 // This version of layout.dart is a shim version of layout2.dart that is backed using CSS and <div>s.
 
 import 'node.dart';
 import 'dart:sky' as sky;
 import 'dart:collection';
 
 // UTILS
 
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       child.parentData = new FlexBoxParentData();
   }
 
   static final Style _displayFlex = new Style._addToCache('display:flex');
   static final Style _displayFlexRow = new Style._addToCache('flex-direction:row');
   static final Style _displayFlexColumn = new Style._addToCache('flex-direction:column');
 
   String stylesToClasses(List<Style> styles) {
     var settings = _displayFlex._className;
     switch (_direction) {
-      case FlexDirection.Row: settings += ' ' + _displayFlexRow._className; break;
-      case FlexDirection.Column: settings += ' ' + _displayFlexColumn._className; break;
+      case FlexDirection.horizontal: settings += ' ' + _displayFlexRow._className; break;
+      case FlexDirection.vertical: settings += ' ' + _displayFlexColumn._className; break;
     }
     return super.stylesToClasses(styles) + ' ' + settings;
   }
 
   void markNeedsLayout() {
     super.markNeedsLayout();
 
     // pretend we did the layout:
     RenderCSS child = _firstChild;
     while (child != null) {
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   print(prefix + node.toString() + _attributes(node));
   var children = node.getChildNodes();
   prefix = prefix + '  ';
   for (var child in children)
     _serialiseDOM(child, prefix);
 }
 
 void dumpState() {
   _serialiseDOM(sky.document);
 }