declaration of DBMS_SQLTUNE.SQLSET_CURSOR cannot be find in oracle's doc

In the following anonymous procedure, we find that

baseline_cursor is defined as DBMS_SQLTUNE.SQLSET_CURSOR". I think it is a built-in data structure.

But i cannot find any description of DBMS_SQLTUNE.SQLSET_CURSOR in the section of package "DBMS_SQLTUNE" in "PL-SQL Packages and Types Reference"

Would you please tell me where can i find it .

Thanks

DECLARE

baseline_cursor DBMS_SQLTUNE.SQLSET_CURSOR;

BEGIN

OPEN baseline_cursor FOR

    SELECT VALUE(p)

    FROM TABLE (DBMS_SQLTUNE.SELECT_WORKLOAD_REPOSITORY(

                  'peak baseline',

                   NULL, NULL,

                   'elapsed_time',

                   NULL, NULL, NULL,

                   30)) p;

    DBMS_SQLTUNE.LOAD_SQLSET(

             sqlset_name     => 'my_sql_tuning_set',