How to use password field in custom field?

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Hi,

I tried to create a user custom field and found out there's a new field type called password.

Online help has following description.

A password is a word or string of characters used for authentication, to prove identity, or gain access to an area or page.

For a custom password field, users can type anything, but they will see “=” for each character they type.

However, I still cannot figure out how to take advantage of it.

Also, the min./max. length didn't work out when user typed the field value.

For example, I set 3 as min. length and 8 as max. length; user still can type only 2 characters in the field via user preference.