Virtual Field Descriptions ========================== Some fields including in the various Mappers don't rely on any actual field in the Model (e.g., ``_action`` or ``batch``). In order to prevent any side-effects when trying to retrieve the value of this field (which doesn't exist), the option ``virtual_field`` is specified for these fields. When the template is instantiated, or whenever the value of the field is required, ``null`` will simply be returned without prying on the Model itself.