Can not be cleaned (check) field in the form if this field is not displayed on the page?

Please tell me, if we're filled form field that is not displayed in the future, it can not be cleaned? For example, the password, let the user enters whatever he wants.
PHP 7
June 10th 19 at 14:56
1 answer
June 10th 19 at 14:58
Found an interesting opinion about the password:
Password validation regular expression?

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