Question on the right way to think about order by

When I think about using order by in a select statement, e.g.

select id, name, price from stuff order by name;

I think of order by as an operator sorting data returned by the select
statement.

When I think about order by in an aggregate statement, e.g.

select string_agg(product, ' | ' order by product) from products;

is it correct to think of order by as a parameter passed to string_agg?