Punycode uses only restricted ASCII characters and numbers (A-z, 0-9) and the hyphen (-). The Punycode schema and the standardization which specifies IDN wire-format to remain in the restricted ASCII repertoire was based on the following advantages:
- Language independent
- Superior in compression
- Compact in code size
- Round-trip safe
- Superior for encoding Chinese/Japanese/Korean characters. (over other ACE schemes evaluated at that time)