ActiveRecord update_attributes with nested hash

Can the parameter hash passed to update_attributes include nested hashes
for child models related through has_many?

For example, if A has many B, can the parameter hash passed to A
include a nested hash for B?

It seems the hash can include attributes for A e.g. one level deep.

Thanks for any advice....

Yes, but update_attributes will look for a child_hash_name= method in
your model. It'll pass in the child hash. Check out the "complex
forms" railscasts--that goes over everything you need.