TYPO3 Core

I want to hide or unhide fields in TCA with displayCond by a multi-value field. So i have a field with multiple checkboxes like that:

'content' => array(
'label' => '...',
'config' => array(
'type' => 'check',
'items' => array(
array('Content A', ''),
array('Content B', ''),
array('Content C', ''),
),
)
),

I also have three content fields like that:

'content_a' => array(
'label' => '...',
'displayCond' => 'FIELD:content:BIT:1',
'config' => array(
'type' => 'text',
)
),
'content_b' => array(
'label' => '...',
'displayCond' => 'FIELD:content:BIT:2',
'config' => array(
'type' => 'text',
)
),
'content_c' => array(
'label' => '...',
'displayCond' => 'FIELD:content:BIT:4',
'config' => array(
'type' => 'text',
)
),

For making that work, i had to add the following lines to class.t3lib_tceforms.php in method isDisplayCondition - case FIELD.