class Mail::ContentTransferEncodingField

def self.normalize_content_transfer_encoding(value)
  case value
  when /7-?bits?/i
    '7bit'
  when /8-?bits?/i
    '8bit'
  else
    value
  end
end

def self.singular?
  true
end

def do_decode
  encoding
end

def do_encode
  "#{name}: #{encoding}\r\n"
end

def element
  @element ||= Mail::ContentTransferEncodingElement.new(value)
end

def encoding
  element.encoding
end

def initialize(value = nil, charset = nil)
  super self.class.normalize_content_transfer_encoding(value), charset
end