code: def _formatter_callback_factory():  # pragma: no cover
      
      includes = []
      exercise_url_template = '{baseUrl}/api/exercises?q={field}:"{{itemCode}}"'
      settings = get_current_registry().settings
      exercise_base_url = settings.get('embeddables.exercise.base_url', None)
      exercise_matches = [match.split(',', 1) for match in aslist(
          settings.get('embeddables.exercise.match', ''), flatten=False)]
      exercise_token = settings.get('embeddables.exercise.token', None)
      mathml_url = settings.get('mathmlcloud.url', None)
      memcache_servers = settings.get('memcache_servers')
      if memcache_servers:
          memcache_servers = memcache_servers.split()
      else:
          memcache_servers = None
  
      if exercise_base_url and exercise_matches:
          mc_client = None
          if memcache_servers:
              mc_client = memcache.Client(memcache_servers, debug=0)
          for (exercise_match, exercise_field) in exercise_matches:
              template = exercise_url_template.format(
                  baseUrl=exercise_base_url, field=exercise_field)
              includes.append(exercise_callback_factory(exercise_match,
                                                        template,
                                                        mc_client,
                                                        exercise_token,
                                                        mathml_url))
      return includes
docs: Returns a list of includes to be given to `cnxepub.collation.collate`.