Evaluation of if conditions

Hi,

How does the IF statement evaluate conditions?  Does it evaluate conditions
following their declaration order from left to right?  In case of
or-conditions, does the IF statement stop evaluating conditions whenever a
first or-condition is true?

The following snippet seems to be invalid, which let me think that PL/PGSQL
evaluates all the conditions:
 IF (TG_OP = 'INSERT') OR    (OLD.bar = ...) THEN   statement END IF;

Should be rewritten as (for example):
 IF (TG_OP = 'INSERT') THEN   statement ELSIF (OLD.bar = ...) THEN   statement END IF;


Regards,

--
Daniel