r a
          "<code title="U+0027 APOSTROPHE">'</code>"
          character.</li>
          <li>A
          <a href="syntax.html#permitted-system-ID" id="permitted-system-ID_xref1">permitted system ID</a>
</li>
          <li>A matching <i>quote mark (system ID)</i>, identical to the
          <i>quote mark (system ID)</i> used earlier (either a
          "<code title="U+0022 QUOTATION MARK">"</code>"
          character or a
          "<code title="U+0027 APOSTROPHE">'</code>"
          character).</li>
  