code: public function isEnabled($field)
      {
          return !isset($this->fields[$field]['enabled']) || (bool) $this->fields[$field]['enabled'];
      }
docs: Is a field enabled?
  
  Returns true, if
  - There is no customized $field.
  - The $field spec does not have the key 'enabled'
  - The key 'enabled' is NOT TRUE.
  
  @param string $field
  
  @return bool