See the output of the following two one-liners:

perl -MO=Xref -e "my @array = sort { $a <=> $b } ( 2, 8, 3 );"
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perl -MO=Xref = "local ( $a, $b ); my @array = sort { $a <=> $b } ( 2,
+ 8, 3 );"
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The first example results in crossreference output that essentially makes no mention of $a and $b.

The second example results in crossreference output that includes $a and $b under the package main namespace.