Right now I am trying build a knowledge base using website_forum and  website_forum_doc module. I need to allow the anonymous user(vistor) to post a question. I tried to modify the ACL list and gave the 'Other Extra Rights / Public' group create permission to 'forum.post.public'. But it does not work. So I infer(think) the anonymous user does not belong to the 'Other Extra Rights / Public' group, but is there a group for anonymous user on the website?