use strict;
use vars '$x';
$x = 3;

sub critical {
  my $w = 50;
  # my $x = 100;            # oops: commented out by mistake
  # my $y = 200;
  my $y = 300;
  frobnicate( $w, $x, $y ); # that's the global $x in there!
}

##</code><code>##

use strict;
$MyModule::x = 3;

# ...
sub critical {
  my $w = 50;
  # my $x = 100;            # oops: commented out by mistake
  # my $y = 200;
  my $y = 300;
  frobnicate( $w, $x, $y ); # won't compile
}

##</code><code>##

sub that_uses_global_x_heavily {
  our $x;                   # we drop the formalities locally
  foobar( $x );
  # ...
  $x = tweak( $x );
  # ...
  and_one_more_thing( $x );
  # ...
}