Html – What are standards for characters allowed in text fields

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What are the typical characters allowed in text fields in a new user sign-up? Are there www standards? Especially interested in Username and Password character types allowed.

Best Solution

Don't restrict password characters. The more characters available, the more secure passwords can be. There's no good reason to forbid spaces, for example, in a password.

For usernames, it depends on where they will be displayed. If you plan to give users there own profile URL, you would want to limit characters much more than if not.

Just don't forget to escape user inputs when you output them again.