In Dict.to_str() and List.to_str() we use json.dump to get a value. However,
JSON includes surrogate escapes in the dumped values, which breaks round trips.
>>> yaml.load(json.dumps({'\U00010000': True}))
{'\ud800\udc00': True}
>>> yaml.load(json.dumps({'\U00010000': True}, ensure_ascii=False))
yaml.reader.ReaderError: unacceptable character #x10000: special characters are not allowed
See:
https://stackoverflow.com/a/38552626/2085149https://news.ycombinator.com/item?id=12798032