itemref

<div itemscope id="amanda" itemref="a b"></div>
<p id="a">Name: <span itemprop="name">Amanda</span></p>
<div id="b" itemprop="band" itemscope itemref="c"></div>
<div id="c">
  <p>Band: <span itemprop="name">Jazz Band</span></p>
  <p>Size: <span itemprop="size">12</span> players</p>
</div>

{
  "@id": "amanda",
  "name": "Amanda",
  "band": {
    "@id": "b",
    "name": "Jazz Band",
    "size": 12
  }
}