my $x;                <- this one.

{
   my $y;             <- not this one.
   ...
}

{
    my $z;            <- this one.
    sub f { ... }
}

##</code><code>##

my $x = 'shadowed';      # <- invisible
{
    my $x = 'shadowing'; # <- visible
    sub f { say "I only see the \$x that's $x." };
}