r collation to use, so as to change the sort
   ordering that determines which values fall into a given range.
  </p><p>
   If the subtype is considered to have discrete rather than continuous
   values, the <code class="command">CREATE TYPE</code> command should specify a
   <code class="literal">canonical</code> function.
   The canonicalization function takes an input range value, and must return
   an equivalent range value that may have different bounds and formatting.
   The canonical output for two r