| Code | Meaning |
| OK | Initial state, no error |
| RD_LEAD_INVAL | Invalid UTF-8 leading octet found |
| RD_CONT_INVAL | Invalid UTF-8 continuation octet found |
| RD_EOF | End of file, input failed |
| RD_NONSHORT | Nonshortest UTF-8 encoding found |
| RD_UNICODE_INVAL | Invalid Unicode code-point found |
| RD_OVERFLOW | Overflow, internal UTF-32 character type too small |
| WR_EOF | End of file, output failed |
| WR_UNICODE_INVAL | Invalid internal UTF-32 character |