What is the format of pokemmo user name?

The user name format of the game is as follows:

User name is between 4 and 15. Only letters or numbers can be used, and the first character must be a letter.

Pokemmo is a lovely multiplayer game developed by pokemmo.eu based on JAVA engine. This game has the most maps in the world. By 2023, * * * will open five regional plates.