To add a custom field as a search option on an Interface as a drop-down list that contains the field's unique values, follow these steps.
Open the Interface settings of the desired Interface by clicking Interfaces, then the name of the interface.
Expand the Form Settings collection and find the Search Form setting.
Click [MetaLocator Fields] to reveal a list of available MetaLocator field names followed by any custom fields. Selecting from this list inserts the markup for that field into the search form.
The [Source] button toggles to reveal/conceil the markup code which might also include HTML.