How can I validate multiple object properties and then apply a style with a tooltip on one of my form elements?
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This is a WPF/MVVM project. I am using the MS Enterprise Library Validation Application Block v5.0. 

The requirement is that if the value of a combobox is "Facilities" or "Other" then the Comment field must have a value.

That said, I created a customer validator and I am performing validation in this manner:
    
    ValidationResults results = Validation.Validate<Annotation>(this.Annotation);

There are other error possibilities and those are covered with the standard VAB attributes.

This seems to be working fine. So, now, if I have an error condition, it could be any one of the rules and I have the ValidationResults collection available to interrogate in order to determine which property has the error. However, I am having trouble with applying a style for a specific element when this occurs. At one point, I was using property level validation for a given control but that doesn't work when I need to compare multiple properties for one validation rule.

    vab:Validate.BindingForProperty="Text"

The property above and this style work for a simple single property validation like a StringLenghtValidator.This doesn't work in my scenario. 

    <Style x:Key="textBoxInError" TargetType="{x:Type TextBox}">            
            <Setter Property="Background" Value="White"/>
            <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>

How can I get the Comments textbox to have a certain style after the multiple property custom validator reports an error?