How to combine imported and local resources in WPF user control

I figured it out. The solution involves MergedDictionaries, but the specifics must be just right, like this:

<UserControl.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="ViewResources.xaml" />
        </ResourceDictionary.MergedDictionaries>
        <!-- This works: -->
        <ControlTemplate x:Key="validationTemplate">
            ...
        </ControlTemplate>
        <style x:key="textBoxWithError" TargetType="{x:Type TextBox}">
            ...
        </style>
        ...
    </ResourceDictionary>
</UserControl.Resources>

That is, the local resources must be nested within the ResourceDictionary tag. So the example here is incorrect.