Nested Object

[FabioTeixeira]

Hi there,
I'm trying to do a schema with nested objects and I want to make some fields inside the object required.
As an example,

type: 'object',
person:{
    type: 'object',
    description:{
        firstName:{
               type: 'string',
               length: 2           
                         }
 }
}

How can i make 'firstName' required?
cumps