---------------------------------------------------------
$this && $that   |    If $this is true, and $that is true
                 |    return the value of the last
                 |    expression evaluated ($that).
-----------------+---------------------------------------
$this || $that   |    If $this evaluates true, stop 
                 |    evaluating, we're done.  Otherwise
                 |    evaluate $that for truthfulness.
                 |    If $that evaluates true, return 
                 |    the value of $that.
---------------------------------------------------------