What do 3 dots/periods/ellipsis in a relay/graphql query mean? : <p>The <a href="https://facebook.github.io/relay/docs/graphql-object-identification.html#content" rel="noreferrer">relay docs</a> contain this fragment:</p>

<pre><code>query RebelsRefetchQuery {
  node(id: "RmFjdGlvbjox") {
    id
    ... on Faction {
      name
    }
  }
}
</code></pre>

<p>What does this <code>... on Faction</code> on syntax mean?</p>
