C# XamDateTimeEditor（基础设施）格式/掩码

此格式不起作用，并且遮罩不显示一天中的前3个字母。我想展示面具上的前三个字母：

<editors:XamDateTimeEditor  
  Width="200" 
  Height="30" 
  HorizontalAlignment="Left" 
  Margin="15,15,0,0" 
  InvalidValueBehavior="RetainValue"
  ToolTip="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" 
  Mask="ddd"
  DateValue="{Binding Date ,Mode=TwoWay,UpdateSourceTrigger=Explicit,ValidatesOnDataErrors=True}"
  LostFocus="UIElement_OnLostFocus"
  ExecutedCommand="XamMaskedEditor_OnExecutedCommand"
  KeyUp="UIElement_OnKeyUp"
  AutoFillDate="MonthAndYear" 
  Grid.Row="2" 
  Grid.Column="1" 
  SpinButtonDisplayMode="Always" 
  SpinWrap="True" 
  SpinIncrement="1d" 
  ValueType="{x:Type sys:DateTime}">
  <editors:XamDateTimeEditor.ValueConstraint>
    <editors:ValueConstraint 
       Nullable="true" 
       ValidateAsType="DateTime"/>
    </editors:XamDateTimeEditor.ValueConstraint>
    <i:Interaction.Behaviors>
      <behaviors:DateTimeEditorFocusBehaviour/>
    </i:Interaction.Behaviors>
  </editors:XamDateTimeEditor>