[gitlab api] what's the access level mean?

In the members api: /projects/:id/members,
here is what the reponse looks likes:

{
  "id": 1,
  "username": "raymond_smith",
  "name": "Raymond Smith",
  "state": "active",
  "avatar_url": "https://www.gravatar.com/avatar/c2525a7f58ae3776070e44c106c48e15?s=80&d=identicon",
  "web_url": "http://192.168.1.8:3000/root",
  "expires_at": "2012-10-22T14:13:35Z",
  "access_level": 30
}

For the access_level, do we have a document for it?