code: protected function handleLoadCallback($field, $value)
      {
          // Load callback.
          if (isset($field['load_callback']) && is_array($field['load_callback'])) {
              foreach ($field['load_callback'] as $callback) {
                  $this->import($callback[0]);
                  $value = $this->{$callback[0]}->{$callback[1]}($value, $this);
              }
          }
  
          return $value;
      }
docs: Handle the onload_callback.
  
  @param array $field The field information.
  
  @param mixed $value The value.
  
  @return mixed