What are valid username conventions?

Valid username conventions typically include the following rules, although they can vary by system:

1. Character Set: Usernames usually consist of lowercase letters (a-z), numbers (0-9), and sometimes underscores (_). Some systems may allow hyphens (-) as well.

2. Length: Usernames often have a minimum and maximum length. Commonly, they must be at least 3 characters long and can be up to 32 characters or more, depending on the system.

3. No Special Characters: Most systems do not allow special characters (e.g., @, #, $, %, &, etc.) in usernames.

4. No Spaces: Usernames typically cannot contain spaces.

5. No Leading Numbers: Some systems do not allow usernames to start with a number.

6. Case Sensitivity: Usernames may be case-sensitive or case-insensitive, depending on the system.

7. Uniqueness: Usernames must be unique within the system, meaning no two users can have the same username.

Always check the specific requirements of the system you are using, as they may have their own set of rules.