Adding of namespace in tamino

Does tamino allows us to add extra namespace beside the usual xs, and tsd?
On trying to add in an extra namespace, it give the error , the current namespace is not allowed in the context.

Anybody has any idea?

No extra namespace is permitted as TSD3 does not support xs:import. However you may declare foreign namespace sections in your schema with xs:any or xs:anyAttribute. Please see this discussion.