How to show Tooltip immediately without hovering of mouse? WPF, TextBox, IDataErrorInfo

Question

I've searched in the Internet for my obvious question and I haven't found asnwers. I've read this article , this and this.

I've implemented IDataErrorInfo and user can see an error if mouse is hovered over textbox. However, I would like to show immediately when error occurs without hovering mouse. I have a canonical data template:

<Style TargetType="TextBox">
    <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="true">
            <Setter Property="ToolTip"
                    Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                    Path=(Validation.Errors)[0].ErrorContent}"/>
        </Trigger>
    </Style.Triggers>
</Style>

My question is that how to avoid need to hover over the edge to get the ToolTip to display?