diff --git a/doc/src/sgml/rangetypes.sgml b/doc/src/sgml/rangetypes.sgml
new file mode 100644
index 3a034d9..c1c210e
*** a/doc/src/sgml/rangetypes.sgml
--- b/doc/src/sgml/rangetypes.sgml
*************** SELECT isempty(numrange(1, 5));
*** 131,159 ****
    <title>Infinite (Unbounded) Ranges</title>
  
    <para>
!    The lower bound of a range can be omitted, meaning that all points less
!    than the upper bound are included in the range. Likewise, if the upper
!    bound of the range is omitted, then all points greater than the lower bound
!    are included in the range. If both lower and upper bounds are omitted, all
!    values of the element type are considered to be in the range.
!   </para>
! 
!   <para>
!    This is equivalent to considering that the lower bound is <quote>minus
!    infinity</quote>, or the upper bound is <quote>plus infinity</quote>,
!    respectively.  But note that these infinite values are never values of
!    the range's element type, and can never be part of the range.  (So there
!    is no such thing as an inclusive infinite bound &mdash; if you try to
!    write one, it will automatically be converted to an exclusive bound.)
    </para>
  
    <para>
!    Also, some element types have a notion of <quote>infinity</quote>, but that
!    is just another value so far as the range type mechanisms are concerned.
!    For example, in timestamp ranges, <literal>[today,]</literal> means the same
!    thing as <literal>[today,)</literal>.  But <literal>[today,infinity]</literal> means
!    something different from <literal>[today,infinity)</literal> &mdash; the latter
!    excludes the special <type>timestamp</type> value <literal>infinity</literal>.
    </para>
  
    <para>
--- 131,156 ----
    <title>Infinite (Unbounded) Ranges</title>
  
    <para>
!    The lower bound of a range can be omitted, meaning that all
!    values less than the upper bound are included in the range, e.g.,
!    <literal>(,3]</literal>. Likewise, if the upper bound of the
!    range is omitted, then all values greater than the lower bound are
!    included in the range. If both lower and upper bounds are omitted,
!    all values of the element type are considered to be in the range.
!    Specifying a missing bound as exclusive is automatically converted
!    to inclusive, e.g., <literal>[,]</literal> is automatically converted
!    to <literal>(,)</literal>.  You can think of these missing values as
!    +/-infinity, but they are special range type values and are considerd
!    to be beyond any range element type's +/-infinity values.
    </para>
  
    <para>
!    Element types that have a notion of <quote>infinity</quote>
!    can use it as explicit bound values.  For example, for timestamp
!    ranges, <literal>[today,infinity)</literal> excludes the special
!    <type>timestamp</type> value <literal>infinity</literal>, while
!    <literal>[today,)</literal>, <literal>[today,]</literal>, and
!    <literal>[today,infinity]</literal> include it.
    </para>
  
    <para>