DJ-Classifieds gives the possibility to create a group of custom fields in the category, contact, profile/registration, and ask form fields and assign them to Joomla groups.
This way, you can display different fields for different groups.
It is a kind of category for extra fields. When creating an additional field, you can select the field group it should belong to, so you can group custom fields, and with the settings available in the field group, you can show/hide this set of extra fields for specific users.
Each custom field that is assigned to a Fields Group gets the CSS class that can be used for styling.
Now when editing a field group field you can choose between:
Category and contact field groups
Profile/registration field groups
Ask form fields
For the ask form fields option, the "access" option disappears because they are always displayed in the form, so access is not applicable.