module ActiveModel::Type

def default_value # :nodoc:

:nodoc: 
def default_value # :nodoc:
  @default_value ||= Value.new
end

def lookup(...) # :nodoc:

:nodoc: 
def lookup(...) # :nodoc:
  registry.lookup(...)
end

def register(type_name, klass = nil, &block)

symbol by {attribute}[rdoc-ref:Attributes::ClassMethods#attribute].
Add a new type to the registry, allowing it to be referenced as a 
def register(type_name, klass = nil, &block)
  registry.register(type_name, klass, &block)
end