Why do many websites not allow usernames to begin with numbers? Passwords are not allowed to start and end with spaces? Is this a technical reason? ?

I think this is completely unnecessary.

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I think this is completely unnecessary.

The reason why you don’t use spaces at the beginning and end is probably to avoid mistyping

How do you distinguish between full-width spaces and half-width spaces?

It is difficult to verify the number of spaces

Generally, spaces at the beginning and end will be filtered out.

When your service supports Mobile phone number login, you will know why

conflicts with UID. Generally, you can see some user information by entering the UID in the address bar. If the username is also all numeric, the system does not know whether it is the username or UID. Back-end logic processing is also relatively troublesome.

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