Using PL/pgSQL to Properly Define A Trigger

I am using PostgreSQL version 8.0. The manual (pages 589 - 590), which describes this process,
I think needs to clarified with an example. 
 
Based on the trigger example (given on p. 590), I am assuming that the trigger variables (given on
p. 589) would be filled in by trigger as follows; can anyone confirm?
 
NEW: contains the row the trigger is asking the emp_stamp() to act on
OLD: not applicable to example 35-1 on p. 590
TG_NAME:  emp_stamp
TG_WHEN:  BEFORE
TG_LEVEL:  ROW
TG_OP: INSERT or UPDATE     -- this may be incorrect !
TG_RELID:                                  -- not sure what this is; does trigger get OID from a system 
                                                         table for name in TG_RELNAME ?
TG_RELNAME:  emp
TG_NARGS: 0                           -- not sure how to count 'arguments', am guessing it is '0', 
                                                       because procedure was called as empstamp() [no args]
TG_ARGV[] :     -- no arguments (TG_NARGS) appear to be passed in this example, so I 
       assume this value would be null. If two arguments were passed, how would they appear 
       to the function? Single quoted, and comma separated - e.g. 'xxxxxxx','xxxxxxxx' ?