title: php, check if a key exists, but it can be multiple keys
body: <p>How to check if a key exists in array, but it can be multiple key?
  I meant:</p>
  
  <pre><code>$a['b'] = 'Im exists!';
  var_dump (isset($a['b']));
  </code></pre>
  
  <p>but my case is a but complicated:</p>
  
  <pre><code>$a['c'] = 'c';
  $a['xxc'] = 'value';
  $a[2][4] = 'more complex!';
  $a['b']['d']['g'] = 4;
  </code></pre>
  
  <p>at this point, isset() wont work, but neither array_key_exists. Then how to check, if I want to know if [2][4] exists, or ['b']['d']['g'] does?</p>