private function _get_value($args){
    if ( $this->id ){
      $var =& $this->data;
      foreach ( $args as $a ){
        if ( !isset($var[$a]) ){
          return null;
        }
        $var =& $var[$a];
      }
      return $var;
    }
  }
private function _get_value($args){
    if ( $this->id ){
      $var =& $this->data;
      foreach ( $args as $a ){
        if ( !isset($var[$a]) ){
          return null;
        }
        $var =& $var[$a];
      }
      return $var;
    }
  }
private function _get_value ( $ args ) { if ( $ this -> id ) { $ var = & $ this -> data ; foreach ( $ args as $ a ) { if ( ! isset ( $ var [ $ a ] ) ) { return null ; } $ var = & $ var [ $ a ] ; } return $ var ; } }
Gets a reference to the part of the data corresponding to an array of indexes

```php
$this->_get_value(['index1', 'index2'])
// Will return the content of $this->data['index1']['index2']
```
@param $args
@return null
Gets a reference to the part of the data corresponding to an array of indexes