 functions required by the index method, nor whether the operators and
   functions form a self-consistent set.  It is the user's
   responsibility to define a valid operator family.
  </p><p>
   Refer to <a class="xref" href="xindex.html" title="38.16. Interfacing Extensions to Indexes">Section 38.16</a> for further information.
  </p></div><div class="refsect1" id="id-1.9.3.22.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>na