Renders children of an element and concatenates them.
This renders all children of an element using drupal_render() and then joins them together into a single string.
$element: The structured array whose children shall be rendered.
$children_keys: If the keys of the element's children are already known, they can be passed in to save another run of element_children().
function drupal_render_children(&$element, $children_keys = NULL) {
if ($children_keys === NULL) {
$children_keys = element_children($element);
}
$output = '';
foreach ($children_keys as $key) {
if (!empty($element[$key])) {
$output .= drupal_render($element[$key]);
}
}
return $output;
}