/** @return string http query string
	 * @param array $requestData associative, of string, possibly nested, like $_REQUEST
	 * @param string $param to be used for creating nested multiple values: <param>[<key>]=<value>
	 */ 
	function queryStringFrom($requestData, $param=null) {
		$keyValueSep = '=';
		$paramSep = '&';
		$params = array();
		$cnv = $this->getConverter();
		forEach($requestData as $key => $value) {
			if ($param!==null)
				$key = $param.'['. $key .']';
			
			$params[] = is_array($value) 
				? $this->queryStringFrom($value, $key) 
				: $cnv->urlEncode($key). $keyValueSep. $cnv->urlEncode($value);
		}
	
		return implode($paramSep, $params);
	}