gistfile1.php

<?php

$person = array(
  "person" => array(
    "name" => "Caius"
  )
);
var_dump($person);
/*
  array(1) {
    ["person"]=>
    array(1) {
      ["name"]=>
      string(5) "Caius"
    }
  }
*/


$key = array_keys($person)[0];
var_dump($key);
/*
  string(6) "person"
*/


$caius = $person[$key];
var_dump($caius);
/*
  array(1) {
    ["name"]=>
    string(5) "Caius"
  }
*/