I'd like to propose the following slight rewording for the note about ALTER
TABLE ... ADD table_constraint_using_index. The existing text says one may
"install it [the existing index] as an official constraint".
The "official constraint" phrase sounds like weasel wording to me -- how is
a UNIQUE constraint more "official" than an UNIQUE index? Then "install"
makes it sound like some installation process is going on that you should
be aware of. I like "convert" slightly better instead.
Josh