static function join($glue, array $list, callable $manipulator) {
		$glued = '';
		foreach ($list as $key => $value) {
			$item = $manipulator($key, $value);
			if ($item !== false) {
				$glued .= $glue.$item;
			}
		}

		if ( ! empty($glued)) {
			$glued = substr($glued, strlen($glue));
		}

		return $glued;
	}