public function render($indent = NULL)
	{
		$s = $this->startTag();

		if (!$this->isEmpty) {
			// add content
			if ($indent !== NULL) {
				$indent++;
			}
			foreach ($this->children as $child) {
				if (is_object($child)) {
					$s .= $child->render($indent);
				} else {
					$s .= $child;
				}
			}

			// add end tag
			$s .= $this->endTag();
		}

		if ($indent !== NULL) {
			return "\n" . str_repeat("\t", $indent - 1) . $s . "\n" . str_repeat("\t", max(0, $indent - 2));
		}

		return $s;
	}