pg_views definition format

Hi,

I have a script that automatically generates the SQL to create some
views. I'd like it to check whether its generated SQL matches the SQL
returned by "select definition from pg_views where...". I've guessed
most of the rules just by looking at the output, but I was surprised
to find that some of my views of the form:

select.........from b left join a on a.id=b.id

...were being translated to this:

SELECT..........FROM (B LEFT JOIN a ON ((a.id = b.id)))

...before being stored in the table pg_views is derived from. My
surprise is at the double parentheses around "a.id = b.id". Is that
supposed to be that way? Is it likely to change?

Thanks,
Kev