The API documentation for this feature lags only slightly behind the very best of our API documentation.  Which is to say, there is none.

It's basically syntactic sugar, so that you can do this:

```ruby
  '+*account' => { '+*email'=>'sample@user.com', '+*password'=>'sample_pass' }
```
instead of this:
```ruby
  :subcards =>{
    '+*account' => {
      :subcards =>{
        '+*email'    => { :content => 'sample@user.com' },
        '+*password' => { :content => 'sample_pass' },
      }
    }
  }
```
but the latter is still supported.  in fact, the method you commented on translates the former into the latter.