Restriction at placement level

[aaicoder]

The spec mentioned "The Placement group comprises objects that define the set of allowed ads and behaviors for a given placement. This might include mechanical information (e.g., sizes, supported mime types, and other rendering options), placement details and positioning, and various restrictions lists."

But I don't find where we can define restrictions of Restrictions object for a placement. Looks like Restrictions object only exist in Context object. Is this intended?