, in
   case the desired step size is larger than what the subtype is capable of
   storing.  For instance, a range type over <code class="type">timestamp</code> could be
   defined to have a step size of an hour, in which case the canonicalization
   function would need to round off bounds that weren't a multiple of an hour,
   or perhaps throw an error instead.
  </p><p>
   In addition, any range type that is meant to be used with GiST or SP-GiST
   indexes should define a subtype difference, or <code cla