e.g., <code class="literal">[,]</code> is converted to <code class="literal">(,)</code>.
   You can think of these missing values as +/-infinity, but they are
   special range type values and are considered to be beyond any range
   element type's +/-infinity values.
  </p><p>
   Element types that have the notion of <span class="quote">“<span class="quote">infinity</span>”</span> can
   use them as explicit bound values.  For example, with timestamp
   ranges, <code class="literal">[today,infinity)</co