+-- Anything over 255 characters is an error, so the root will be
+-- parsed:
+--
+-- >>> let big_label = replicate 63 'x'
+-- >>> let big_subdomain = concat $ replicate 5 (big_label ++ ".")
+-- >>> parseTest domain big_subdomain
+-- DomainRoot
+--
+-- But exactly 255 is allowed:
+--
+-- >>> import Data.List ( intercalate )
+-- >>> let big_label = replicate 63 'x'
+-- >>> let big_subdomain = intercalate "." (replicate 4 big_label)
+-- >>> let (Right r) = parse domain "" big_subdomain
+-- >>> length (pretty_show r)
+-- 255
+--