elgg_extract($key, $array, $default=null, bool $strict=true)
Checks for $array[$key] and returns its value if it exists, else returns $default.
if(!isset($id)) $vars['id']
elgg_extract_class(array $array, array|string $existing=[], string $extract_key= 'class')
Extract class names from an array, optionally merging into a preexisting set.