omposite_type :: Parser ByteString
composite_type = fmap sToLower
               $ stringCI "message"
             <|> stringCI "multipart"
             <|> extension_token

composite_type :: Parser ByteString
composite_type = fmap sToLower
               $ stringCI "message"
             <|> stringCI "multipart"
             <|> extension_token
composite_type = fmap sToLower
               $ stringCI "message"
             <|> stringCI "multipart"
             <|> extension_token