@@ -39,16 +39,18 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
3939 </para>
4040
4141 <para>
42- A policy is an expression which is added to the security-barrier
43- qualifications of queries which are run against the table the policy is on,
44- or an expression which is added to the with-check options for a table and
45- which is applied to rows which would be added to the table.
46- The security-barrier qualifications will always be evaluated prior to any
47- user-defined functions or user-provided WHERE clauses, while the with-check
48- expression will be evaluated against the rows which are going to be added to
49- the table. By adding policies to a table, a user can limit the rows which a
50- given user can select, insert, update, or delete. This capability is also
51- known as Row Level Security or RLS.
42+ A policy limits the ability to SELECT, INSERT, UPDATE, or DELETE rows
43+ in a table to those rows which match the relevant policy expression.
44+ Existing table rows are checked against the expression specified via
45+ USING, while new rows that would be created via INSERT or UPDATE are
46+ checked against the expression specified via WITH CHECK. Generally,
47+ the system will enforce filter conditions imposed using security
48+ policies prior to qualifications that appear in the query itself, in
49+ order to the prevent the inadvertent exposure of the protected data to
50+ user-defined functions which might not be trustworthy. However,
51+ functions and operators marked by the system (or the system
52+ administrator) as LEAKPROOF may be evaluated before policy
53+ expressions, as they are assumed to be trustworthy.
5254 </para>
5355
5456 <para>