$0 is set to the whole match, then $1, $2 : preg_replace « String « PHP

$0 is set to the whole match, then $1, $2

    $match = "/the (car|cat) sat on the (drive|mat)/";
    $input = "the cat sat on the mat";
    print preg_replace($match, "Matched $0, $1, and $2\n", $input);

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