Looking through the code I found the DefaultEffector class merge_effects() method that processes the policy_effect. Suprisingly from the code there is only 4 possible values for the policy_effect and they are specific strings and not actual code as I was expecting. The 4 possible values are:

• "some(where (p_eft == allow))"
• "!some(where (p_eft == deny))"
• "some(where (p_eft == allow)) && !some(where (p_eft == deny))"
• "priority(p_eft) || deny"