PHP Integer数组索引真的是数字吗？

Consider this example

考虑这个例子

<?php
    $test = array("00"=>"A","B","C","D","E");
    print_r($test);
    echo "<br>";

    echo $test[0];
    echo "<br>";
    echo $test["0"];
    echo "<br>";

    echo $test["00"];
    echo "<br>";
    echo $test[00];
?>
<?php
    $tes