In-law apartment

To search for properties that may have an in-law apartment, go to Search> Residential> SF & CO Search.  

There is a Has In-Law Apartment field in the center column (in the Property Characteristics section):

Click within the blank field to display your options (Yes, Possible, No):

Put a check in the box(es) that apply, then click OK. 
Note: the field allows you to choose more than one option.