way to custom sort column by fixed strings, then by field's content

and I would like them to sort in that order.

I tried:
select sti.description, sc.description from scene_thing_instances sti join scenes sc on sti.scene_id = sc.scene_id
  order by CASE sc.description
            when (sc.description = 'absolute root'::text) then 1
            when (sc.description ilike 'root%') then  2
            else 3
           END;

I was starting with this, and was going to add perhaps another case statement.