use strict;        # apply all possible restrictions

use strict 'vars'; # restrict unsafe use of variables for rest of block
use strict 'refs'; # restrict unsafe use of references for rest of block
use strict 'subs'; # restrict unsafe use of subroutines for rest of block

no strict 'vars';  # void restrictions on variables for rest of block
no strict 'refs';  # void restrictions on references for rest of block
no strict 'subs';  # void restrictions on subroutines for rest of block
*****
use strict 'refs';
$ref = \$foo;
print $$ref;        # ok
$ref = "foo";
print $$ref;        # run-time error; normally ok
*****
use strict 'vars';
use vars '$foe';
$SomePack::fee = 1;  # ok, fully qualified
my $fie = 10;        # ok, my() var
$foe = 7;            # ok, pseudo-imported by 'use vars'
$foo = 9;            # blows up--did you mistype $foe maybe?
*****
use strict 'subs';

$SIG{PIPE} = Plumber;     # blows up (assuming Plumber sub not defined yet)
$SIG{PIPE} = "Plumber";   # okay, means "main::Plumber" really
$SIG{PIPE} = \&Plumber;   # preferred form
*****
use strict;      # or just:  use strict subs;
[ ... ]
no strict subs;  # WRONG!  Should be:  no strict 'subs';
[ ... ]
*****
use subs qw(sub1 sub2 sub3);
sub1 $arg1, $arg2;