docs: def count(cls, slug):
          """get the number of objects in the cache for a given slug
  
          :param slug: cache key
          :return: `int`
          """
          from .models import Content
          # Gets the count for a tag, hopefully form an in-memory cache.
          cnt = cls._cache.get(slug)
          if cnt is None:
              cnt = Content.search_objects.search(tags=[slug]).count()
              cls._cache[slug] = cnt
          return cnt