Mouse over state of RadButton

[Jackey]

Hi team,

I am reading the implicite style of radbutton, and find that the storyborad of mouse over state is below

 

<VisualState x:Name="MouseOver">
                                    <Storyboard>
                                        <DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="OuterMouseOverBorder"/>
                                    </Storyboard>
                                </VisualState>

And my question is why use UIElement.Opacity here instead just Opacity, like other states' storyborad do?

Thanks,

Jingfei