Is given value one that should cause the DB row(s) to be deleted rather than saved?
Not applicable to Fieldtypes that override the savePageField() method with their own implementation, unless they also use this method.
Available since version 3.0.150.
$bool = $fieldtype->isDeleteValue(Page $page, Field $field, mixed $value);
API reference based on ProcessWire core version 3.0.168