Nested attributes for relationships

If I were updating / creating a "post" and I also wanted to create / update tag id 3 in the example below, should that be possible (i.e. similar to nested attributes in active record).

Probably a bit of a bad example, but hopefully you get the idea ?

I am finding that each entry in "data" in the relationships must only contain id and type. Nowhere have I yet seen how to do this in json_api in general, not just in this gem so maybe it is not possible. In which case, I guess I would need to create / update the tag seperately, but then I may need to worry about rolling it back if the creation / update of the post did not succeed etc...

post '/posts',
  {
    'posts' => {
      'attributes' => {
        'title' => 'A great new Post'
      },
      'relationships' => {
        'tags' => {
          'data' => [
              {type: 'tags', id: 3, attributes: {name: "New Tag Name"}},
              {type: 'tags', id: 4}
            ]
        }
      }
    }
  }

No source file, test, or entry point is named. Start by reviewing the existing relationship create/update handling and the JSON:API rules for relationship data, then establish whether nested attributes are supported. Done should be a clear decision with defined request behavior and transaction or rollback expectations.