Re: cast to domain with default collation issue.

I wrote:
> Perhaps this should be documented more clearly, but it's not obviously
> wrong. If the domain declaration doesn't include an explicit COLLATE
> then casting to the domain doesn't create an explicit collation
> requirement. (That is, the domain *doesn't* have a specific
> collation attached to it, any more than type text does.)

Perhaps we could improve matters like this?

diff --git a/doc/src/sgml/ref/create_domain.sgml b/doc/src/sgml/ref/create_domain.sgml
index 81a8924926..e4b856d630 100644
--- a/doc/src/sgml/ref/create_domain.sgml
+++ b/doc/src/sgml/ref/create_domain.sgml
@@ -94,7 +94,8 @@ CREATE DOMAIN <replaceable class="parameter">name</replaceable> [ AS ] <replacea
<listitem>
<para>
An optional collation for the domain. If no collation is
- specified, the underlying data type's default collation is used.
+ specified, the domain has the same collation behavior as its
+ underlying data type.
The underlying type must be collatable if <literal>COLLATE</literal>
is specified.
</para>

regards, tom lane