Override or insert variables into the block template.

File

drupal-7.x/themes/bartik/template.php, line 120

Code

function bartik_preprocess_block(&$variables) {
  // In the header region visually hide block titles.
  if ($variables['block']->region == 'header') {
    $variables['title_attributes_array']['class'][] = 'element-invisible';
  }
}