Preprocess variables for region.tpl.php
Prepares the values passed to the theme_region function to be passed into a pluggable template engine. Uses the region name to generate a template file suggestions. If none are found, the default region.tpl.php is used.
region.tpl.php
function template_preprocess_region(&$variables) {
// Create the $content variable that templates expect.
$variables['content'] = $variables['elements']['#children'];
$variables['region'] = $variables['elements']['#region'];
$variables['attributes']['class'][] = 'region';
$variables['attributes']['class'][] = drupal_html_class('region-' . $variables['region']);
$variables['theme_hook_suggestions'][] = 'region__' . $variables['region'];
}