TYPO3 Core

Adding a placeholder attribute to the FormEngine would improve user experience by giving the editor some hints about possible values

Example:

'background_color' => array(
    'label' => 'label',
    'config' => array(
        'type' => 'input',
        'eval' => 'trim',
        'placeholder' => '#0000ff'
    ),
),

would result in:

<input name="background_color" placeholder="#0000ff" />