extending pg_type

hi there,

I would like to extend the Postgres system catalog pg_types with the two
fields wwwin and wwwout for interfacing all Postgres types with HTML. Is
this possible? Are there too many changes necessary to make this work?
Is this the straight forward way to use the overloading and resolution
mechanisms for new system wide attributes?

Entity-relationship-diagrams form a kind of net similiar to that of
hypertexts. Thus a thight integration of HTML into Postgres and the use
of Apache will make it possible to browse arbitrary databases through
WWW and to easily customize the generated user interface by a mere
selection of the generating primitives and constructors.

Thanks for any suggestions.
Wolfgang