tml_validate_new_user_password()

function tml_validate_new_user_password( $errors = null ) {
    // phpcs:disable WordPress.Security.NonceVerification.Missing -- mirrors WP core's own registration password validation (register_new_user()), which has no nonce of its own.

    if ( empty( $errors ) ) {
        $errors = new WP_Error();
    }

    if ( tml_allow_user_passwords() ) {
        if ( empty( $_POST['user_pass1'] ) || empty( $_POST['user_pass2'] ) ) {
            $errors->add( 'empty_password', __( '<strong>Error:</strong> Please enter a password.', 'theme-my-login' ) );

        } elseif ( false !== strpos( stripslashes( $_POST['user_pass1'] ), '\\' ) ) {
            $errors->add( 'password_backslash', __( '<strong>Error:</strong> Passwords may not contain the character "\\".', 'theme-my-login' ) );

        } elseif ( $_POST['user_pass1'] !== $_POST['user_pass2'] ) {
            $errors->add( 'password_mismatch', __( '<strong>Error:</strong> Passwords don&#8217;t match. Please enter the same password in both password fields.', 'theme-my-login' ) );
        }
    }
    // phpcs:enable WordPress.Security.NonceVerification.Missing

    return $errors;
}

View src/includes/functions.php, line 737 on GitHub