Note: This doesn't take magic into account. The bitwise ops sure do.

print is_num($|), "\n";   # 0
$|=1;
print is_num($|), "\n";   # 0
print 1   | "A", "\n";
print "1" | "A", "\n";
print $|  | "A", "\n";    # Acts as if $| is numeric
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Note: SvUOK(x) will always be false if SvIOK(x) is false, and SvNIOK(x) is more efficient than SvIOK(x) || SvNOK(x).