Example of using AdditionalMetadata in MVC 3

According to the documentation:

You can use the AdditionalMetadataAttribute class to populate the ModelMetadata.AdditionalValues dictionary for a model property.

...

This metadata is made available to any display or editor template when a product view model is rendered. It is up to you as application developer to interpret the metadata information.

So let's make use of it in the view:

<h2>
    @ModelMetadata.FromLambdaExpression(x => x.Title, ViewData).AdditionalValues["Tooltip"]
</h2>