class Psych::Visitors::RestrictedYAMLTree

def accept target
  if !@aliases && @st.key?(target)
    raise BadAlias, "Tried to dump an aliased object"
  end
  unless Symbol === target || @permitted_classes[target.class]
    raise DisallowedClass.new('dump', target.class.name || target.class.inspect)
  end
  super
end