Lexical scopes of control structures are not bounded precisely by the braces that delimit their controlled blocks; control expressions are part of that scope, too. Thus in the loop the scope of $line extends from its declaration throughout the rest of the loop construct (including the continue clause), but not beyond it

  while (my $line = <>) {
        $line = lc $line;
    } continue {
        print $line;
    }
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So A my declares the listed variables to be local (lexically) to the enclosing block, file, or eval.