CASE Statement Syntax - ??? never saw befor.

Hi, Everyone:

I have never come accross this syntax in a CASE statement before; ... END = 1 ...
please see below.  

What does it mean?

Thank you,

      SELECT TOP (@maxIndexSize) @requestID
            , svo.MlsNum
      FROM
            mls_unified_svo_tbl svo (nolock)
      WHERE
            svo.LoadOnInternet = 1
            AND svo.std IS NOT NULL
            AND svo.snd IS NOT NULL      
            AND (svo.Status IN (5, 30, 45)
                        OR
                        (svo.Status IN (10, 20)
                              AND DATEDIFF(day, svo.StatusDate, GETDATE()) < 365
                         )
                  )
                  
            AND
                  CASE WHEN @request.exist('/searchRequest/mlsNumber') = 0
                        THEN 1
                        ELSE
                              CASE WHEN svo.MlsNum = @request.value('(/searchRequest/mlsNumber)[1]', 'varchar(20)') THEN 1
                              ELSE 0
                              END
                        END = 1

            AND
                  CASE WHEN @request.exist('/searchRequest/zipCode') = 0
                        THEN 1
                        ELSE
                              CASE WHEN svo.zip = @request.value('(/searchRequest/zipCode)[1]', 'varchar(500)') THEN 1
                              ELSE 0
                              END
                  END = 1
            
            AND
                  CASE WHEN @request.exist('/searchRequest/city') = 0
                        THEN 1
                        ELSE
                              CASE WHEN svo.city = @request.value('(/searchRequest/city)[1]', 'varchar(50)') THEN 1
                              ELSE 0
                              END
                        END = 1