Currently there is no dedicated support for doing this. However there are few ways how to achieve this.
My preferable is to discuss it in the request description using a markdown formatting of your liking e.g:
### Add a new User [POST]
To add a User send a JSON .....
+ Request (application/json)
Data about user being created. Where age attribute is optional.
+ Body
{
"name": "A name",
"age": 30
}
or perhaps:
To add a User send a JSON .....
+ Request (application/json)
Data about user being created. With following attributes are:
+ `name` ... name of the user
+ `age` (optional) ... age of the user
+ Body
{
"name": "A name",
"age": 30
}
See http://docs.gtdtodoapi.apiary.io Folder Collection resource for a futher example.
You can also always specify a JSON schema describing the body payload. Note dedicated support for discussing message body attributes is in the making (https://github.com/apiaryio/api-blueprint/issues/25)