Provides a standard HTML class name that identifies a page region.
It is recommended that template preprocess functions apply this class to any page region that is output by the theme (Drupal core already handles this in the standard template preprocess implementation). Standardizing the class names in this way allows modules to implement certain features, such as drag-and-drop or dynamic Ajax loading, in a theme-independent way.
$region: The name of the page region (for example, 'page_top' or 'content').
An HTML class that identifies the region (for example, 'region-page-top' or 'region-content').
function drupal_region_class($region) {
return drupal_html_class("region-{$region}");
}