TYPO3 Core

tx_styleguide_inline_1n -> inline_1 -> input_3 TCA:

        'input_3' => [
            'exclude' => 1,
            'label' => 'input_3',
            'description' => 'placeholder=__row|input_1 mode=useOrOverridePlaceholder eval=null default=null',
            'config' => [
                'type' => 'input',
                'placeholder' => '__row|input_1',
                'eval' => 'null',
                'default' => null,
                'mode' => 'useOrOverridePlaceholder',
            ],
        ],

This creates one of those 'placeholder' input fields: A checkbox toggles a read-only input field with a not-read-only input field. This is especially used in FAL inline relations for title and description (allow to override these fields into the sys_file_reference field with a readonly fallback to sys_file_metadata.

• Create styleguide data using the styleguide TCA/records interface with current styleguide master branch (this contains input_3 field).
• edit translated german record on page 'inline 1n' and delete the inline _1 child.
• save
• see the 'shadowed' inline child, indicating that there is an element in default language, that has not yet been localized.
• click 'Synchronize with original language' button.

-> The input_3 placeholder field dos not initialize, both readonly-input and non-readonly-input fields are rendered. see screenshot.