Syntax Error if the BoundNames of |ForDeclaration| contains any duplicate entries.
      </li>
    </ul>
  </emu-clause>

  <emu-clause id="sec-for-in-and-for-of-statements-static-semantics-containsduplicatelabels">
    <h1>Static Semantics: ContainsDuplicateLabels</h1>
    <p>With argument _labelSet_.</p>
    <emu-see-also-para op="ContainsDuplicateLabels"></emu-see-also-para>
    <emu-grammar>
      IterationStatement :
        `for` `(` LeftHandSideExpression `in` Expression `)` Statement
        `for` `