title: YANG - mandatory choice
body: <p>From <a href="https://www.rfc-editor.org/rfc/rfc7950#section-7.9.4" rel="nofollow noreferrer">RFC 7950#7.9.4</a>:</p>
  <blockquote>
  <p>The behavior of the [mandatory] constraint depends on the type of the choice's
  closest ancestor node in the schema tree that is not a non-presence(see Section 7.5.1):</p>
  </blockquote>
  <blockquote>
  <ul>
  <li>If no such ancestor exists in the schema tree, the constraint is enforced.</li>
  </ul>
  </blockquote>
  <blockquote>
  <ul>
  <li>Otherwise, if this ancestor is a case node, the constraint is enforced if any other node from the case exists.</li>
  </ul>
  </blockquote>
  <blockquote>
  <ul>
  <li>Otherwise, it is enforced if the ancestor node exists.</li>
  </ul>
  </blockquote>
  <p>Now: the first and the last point seems to be quite straightforward, but I can't get the second one.</p>
  <p>Is it trying to say that if first <code>non-presence container</code> ancestror is a <code>case</code> node, then the constraint must be enforced if the <code>case</code> has more than one child? Basically, it means that I must enforce the mandatory if the <code>case</code> contains a <code>uses</code>?</p>