Though you're example is perfect, your wording is not. x works also on lists, not on arrays:

$ perl -E'@x=("a".."c");@y=@x x 3;say@y'
333
$ perl -E'@x=("a".."c");@y=(@x)x 3;say@y'
abcabcabc
$
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That is why the extra parens are needed, otherwise the array would be evaluated in scalar context by x and hence returns its length.