-`456-789` : default size, still user freindly and sufficient randomness (for personal data)
-`abc-def-ghj` : long version. alphabets except i, l and o are also valid
## Specs
### Characters
## Perpose
When I considering implementing IDs for users(not for internal system) to specify items, such as GitHub commit hashes or issue numbers, the following issues arose.
- Sequential numbers like Git issues are difficult to implement in distributes systems because collitions are unavoidable.
- Random number like UUID is too long for users
- Short random number like 7-digit commit hash seems good but is is not standardized specification.
