def show_in_nav_for(level=0, icon=None):
    """
    Use as a class / method decorator to flag an exposed object in the site navigation

    @show_in_nav_for(users.guest)
    @expose
    class SubPage:
        ...
    """
    def decorate(f):
        f.show_in_nav = level
        f.icon = icon
        f.exposed = True
        return f
    return decorate