there's a "platform" pattern that i've seen where the idea is that you define things like this:

definition user {}

definition platform {
  relation moderator: user
  permission moderate = moderator
}

definition site {
  relation platform: platform
  relation reader: user
  relation editor: user
  relation owner: user
  relation admin: user

  permission view = edit + reader
  permission edit = delete + editor
  permission delete = owner + admin + platform->moderate
}