COMMENT ON CONSTRAINT ON DOMAIN ?

Hello,

I may be totally missing something, but there seems to be no way 
to create a COMMENT on a domain constraint.  There is

COMMENT ON CONSTRAINT constraint_name ON table_name

but no such thing for domain constraints, which seems like a 
weird omission.  

I couldn't find any relevant discussions on the list; is there a 
technical reason this is not implemented?

Looking at the source, get_object_address() always assumes a 
constraint is a table constraint.  It seems to me that there is 
a relatively easy fix:

COMMENT ON CONSTRAINT constraint_name ON DOMAIN domain_name,

then store constraint subject type (relation vs. domain) in 
objname list, and handle that in get_object_address().

Thoughts?
                        Elvis