unctions are case-insensitive.
      </p>
<p>
        The dots in <code class="computeroutput"><span class="identifier">nan</span><span class="special">(...)</span></code>
        stand for an arbitrary string. The meaning of that string is implementation
        dependent. It can be used to convey extra information about the NaN, from
        the 'payload'. A particular value of the payload might be used to indicate
        a <span class="emphasis"><em>missing value</em></span>, for example.
      </p>
<p>