or declared with our or a special identifier or the symbol/type-glob was already used (i.e. @x and $x)

perldiag#used only once: possible typo

#use strict;
use warnings;

$x=1;
@x=(2);
my $the_variable_I_want_to_check = 3;
our $the_varaible_I_want_to_check = 4;
$^A=5;
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no warnings!