Go to “onOffice > Estates” and edit your estate list. In the field list on the bottom right, expand the field “Property class” by clicking on the arrow on the right.
To add this field to the search as a filter, you can check “Filterable”. Make a few more fields “Filterable”. You can look at your estate list and test how the estate search.
If the setting “Hidden” is checked, the field will not show up in the search form. This is useful for developers who are making template customizations and want to filter this field using query parameters, because for security reasons you need to whitelist which fields can be queried.
For selection fields, the option “Reduce values according to selected filter” will remove values that would lead to no results. For example, imagine that you have filtered for estates with more than three rooms and there are no apartments with that many rooms in your list, only houses. If this option is checked for the field “Property class”, then you can select the value “House”, but “Apartment” will not be available.