Re: SQL:2011 application time

+     <para>
+      If the last column is marked with <literal>PERIOD</literal>,
+      it is treated in a special way.
+      While the non-<literal>PERIOD</literal> columns are treated normally
+      (and there must be at least one of them),
+      the <literal>PERIOD</literal> column is not compared for equality.
+      Instead the constraint is considered satisfied
+      if the referenced table has matching records
+      (based on the non-<literal>PERIOD</literal> parts of the key)
+      whose combined <literal>PERIOD</literal> values completely cover
+      the referencing record's.
+      In other words, the reference must have a referent for its
entire duration.
+      Normally this column would be a range or multirange type,
+      although any type whose GiST opclass has a "contained by" operator
+      and a <literal>referenced_agg</literal> support function is allowed.
+      (See <xref linkend="gist-extensibility"/>.)
+      In addition the referenced table must have a primary key
+      or unique constraint declared with <literal>WITHOUT PORTION</literal>.
+     </para>

typo "referenced_agg", in the gist-extensibility.html page is "referencedagg"
<literal>WITHOUT PORTION</literal> should be <literal>WITHOUT OVERLAPS</literal>

+      While the non-<literal>PERIOD</literal> columns are treated normally
+      (and there must be at least one of them),
+      the <literal>PERIOD</literal> column is not compared for equality.
the above sentence didn't say what is "normally"?
maybe we can do the following:
+      While the non-<literal>PERIOD</literal> columns are treated
+ normally for equality
+      (and there must be at least one of them),
+      the <literal>PERIOD</literal> column is not compared for equality.



+<programlisting>
+Datum
+my_range_agg_transfn(PG_FUNCTION_ARGS)
+{
+    MemoryContext    aggContext;
+    Oid              rngtypoid;
+    ArrayBuildState *state;
+
+    if (!AggCheckCallContext(fcinfo, &aggContext))
+        elog(ERROR, "range_agg_transfn called in non-aggregate context");
+
+    rngtypoid = get_fn_expr_argtype(fcinfo->flinfo, 1);
+    if (!type_is_range(rngtypoid))
+        elog(ERROR, "range_agg must be called with a range");
+
+    if (PG_ARGISNULL(0))
+        state = initArrayResult(rngtypoid, aggContext, false);
+    else
+        state = (ArrayBuildState *) PG_GETARG_POINTER(0);
+
+    /* skip NULLs */
+    if (!PG_ARGISNULL(1))
+        accumArrayResult(state, PG_GETARG_DATUM(1), false, rngtypoid,
aggContext);
+
+    PG_RETURN_POINTER(state);
+}
+
+Datum
+my_range_agg_finalfn(PG_FUNCTION_ARGS)
+{
+    MemoryContext    aggContext;
+    Oid              mltrngtypoid;
+    TypeCacheEntry  *typcache;
+    ArrayBuildState *state;
+    int32            range_count;
+    RangeType      **ranges;
+    int              i;
+
+    if (!AggCheckCallContext(fcinfo, &aggContext))
+        elog(ERROR, "range_agg_finalfn called in non-aggregate context");
+
+    state = PG_ARGISNULL(0) ? NULL : (ArrayBuildState *) PG_GETARG_POINTER(0);
+    if (state == NULL)
+        /* This shouldn't be possible, but just in case.... */
+        PG_RETURN_NULL();
+
+    /* Also return NULL if we had zero inputs, like other aggregates */
+    range_count = state->nelems;
+    if (range_count == 0)
+        PG_RETURN_NULL();
+
+    mltrngtypoid = get_fn_expr_rettype(fcinfo->flinfo);
+    typcache = multirange_get_typcache(fcinfo, mltrngtypoid);
+
+    ranges = palloc0(range_count * sizeof(RangeType *));
+    for (i = 0; i < range_count; i++)
+        ranges[i] = DatumGetRangeTypeP(state->dvalues[i]);
+
+    PG_RETURN_MULTIRANGE_P(make_multirange(mltrngtypoid,
typcache->rngtype, range_count, ranges));
+}

my_range_agg_transfn error message is inconsistent?
 `elog(ERROR, "range_agg_transfn called in non-aggregate context");`
`elog(ERROR, "range_agg must be called with a range");`
maybe just `my_range_agg_transfn`, instead of mention
{range_agg_transfn|range_agg}
similarly my_range_agg_finalfn error is also inconsistent.

my_range_agg_finalfn need  `type_is_multirange(mltrngtypoid)`?